There's a heat wave coming - tips for keeping the tanks cool

As the title suggests what tips have we got for keeping the tank temps down with this predicted heatwave?

It's currently 26 degree's here in sizzling Yorkshire. It's now the hottest part of the day and I'm watching my tank temp closely. My living room faces south and so the sun hits my huge 7ft window at it's hottest point of the day and the room starts to heat up rapidly. Currently my tank is okay at it's regular 25 degree's but I've just closed my blinds and set a cooling fan going. The temperature of the room is slowly dropping so hopefully the tank will remain in the safe level. My angels won't mind a slight rise as at 25 it's on the lower end for them but my cories will be the one's that suffer if it starts to rise.

I have read on other forums about filling a small bottle with water, freezing it and them floating the bottle in the tank... this seems a sensible idea (and an idea I've passed on but not needed to try yet myself) but there's some arguement now that doing that can be harmful to the fish. I've also heard of opening the tank lid but if we have fish likely to jump then this isn't an option.

So ... you have my tip (close the curtains/blinds and set a fan going) has anyone got any other tips

I've been out for a couple of hours and just checked the tank temp and it's shot up to nearly 27 degree's. So now it's lights off and lid open just enough to let some heat out but not enough for the fish to jump out ...

I'm not doing anything different, if the air temp in the fish room reaches 30C (at eye level) then I normally adjust things down a touch to save fuel costs.

Currently at 30.4C air temp and the water temp around 27C.

My Tip: Warmer water can't carry as much oxygen, so a reasonable stocking density, strong air-stone and no direct sunlight should see you through a British heat wave.


I read somewhere that putting a fan in an enclosed room just heats the room up! It might feel colder to a person in the room, but the heat from the motor just increases the heat.

If I were into marine fish, I'm sure I'd be more aware of overheating - but things as they are, I say bring on the sun! let it shine, let it shine, let it shine - a 50% reduction in fuel makes me happy!

Just wondered, if the tank water is cooler than the outside temperature, opening the lid would just serve to allow more hot air to come into contact with the surface of the water, so that would heat it up by drawing off the cold. Heating and cooling is a funny thing and people often think of things the other way around. In this case, it's the cold you're trying to keep in, not the heat you're trying to get out. So really, as daft as it may sound, putting insulation boards around the tank would help to keep the cold in!...and keep the heat out as opposed to get or let the heat out.

Whenever there is a difference in temperature between two things (be they solid, liquid or gas) there is always interaction between the two to equalize the temperatures. Another interesting fact, is that water is the only thing that can exist in three states: a solid (ice), liquid (water) and steam (gas). Nothing else can do this, so water is very special

you're right Dean ... opening the lid just heated it up. Tank lights out, dark room, windows wide open so a breeze is coming in and it's come down to bang on 26 - one degree up from normal but at least 2 degree's down from where it was at it's worse point.

I'm worried about my cories the most ... they don't like it too hot which is why I run the tank at 25 - it's a degree above what they'd prefer but bearable for them. I'm trying to find happy medium.

The cooling fan is off now .. I can't afford to run it for too long as it'll chew through electric. I'm not even going to open the curtains tomorrow now. If I can keep the room cool I've half a chance of keeping the tank temps down. I've also turned my heater down a degree so over night it should fall to 24 degrees - a bit cool for the angels mind - my thinking is if I can lower it over night then when it heats up in the afternoon it might not go as far as it did today. It's all trial and error though so I'm hoping for some more tips if anyone has any

I have an albino cory and I've never really considered keeping it cool. All I can say is that I and others I know, have kept these at 27C for several months without any problems.

I'm sure keeping the curtains closed will help reflect the heat back out.

If there is no other way to cool the air or insulate the tank from the warm air (which is causing the warming) the only other option is to cool the water directly, by adding cooler water to existing water or cooling the existing water indirectly by bringing it into close contact with a coolant (which might also be water). For example:

If you have an external filter, you could drop a few loops into a cold bucket of water (draw off any 'warm' cold water from the tap first) - as the water passes through it, it would be cooled. Add some ice cubes if you don't want to have to keep filling the bucket up. This keeps ice away from the fish. The wider the bore of the tube, the greater the heat loss. The more loops exposed to the cold water, the greater the heat loss. The colder the water, the greater the heat loss. But remember, if the heat loss is very quick, the tank temp will fluctuate and this is not what our fish want. A high flow rate would probably work out better than low imo.

If you don't have an external filter, but have a pump device, you can attach a length of hose and circulate it back into the tank in the same way. For the confused, the tank water runs through the hose, it doesn't mix with the cold water in the bucket.

In both cases, you'd trial how quickly the bucket water warmed up. Maybe refresh the cool water once an hour? if you can constantly refresh the bucket with cool water, even better! but leave the heater running, just in case you overdo it.

There are more costly (perhaps more complicated) and 'less work' ways of cooling a tank, but I'll leave that for the time poor rich folk. Most problems are solved with buckets and hose

Some species of corydoras come from quite cool water and are quite sensitive to high temperatures, whilst others are perfectly happy even into the low 30s.

The worst problem with high temperatures is fluctuation in temperature rather than the high temperatures themselves. For that reason, think very carefully before adopting any strategy to cool the tank. I'd strongly advise against pouring cooler water into the tank directly, as this can cause rapid swings in temperature. I'd also advise against turning heaters off. Heaters have built in thermostats which switch them off when the temperature goes over their set temperature, so turning them off is pointless. Every year, a while after we've had a heat wave we get someone come into the shop having had problems because they forgot to turn the heater back on when the weather cooled.

Turning lights off will help keep the temperature lower. Opening lids does help cool the tank as it allows more evaporation to occur, this can be further improved if you place a desk top fan in a position such that it's blowing air over the surface of the water (but take care to ensure there's no risk of the fan falling into the tank). It's true that if you measure the total heat energy in a room, all a fan does is move air from one place to another and overall adds heat energy from it's own motor. However because of the cooling effect of evaporation, a fan will cool the tank, at the expense of raising the overall room temperature slightly.

Another approach is to freeze plastic drink bottles of water in a freezer, and then float them on the top of the tank. Take care to leave a reasonable air space in the bottle before freezing, to avoid the risk of it cracking as the ice expands. If using this approach, you need to be dedicated & persistent if you are to avoid causing big swings in the temperature, which as I've already said, can be more harmful than the high temperature itself.

Now I've heard about the frozen plastic bottle and I've recommended it to others in the past but now there's a row going on on one the other forums I'm a member of saying that it's a dangerous path to go down.

They are saying that the frozen bottle can have the tank swinging wildly the other way causing stress to the fish and potentially causing white spot. They are also saying that if any of the fish swim into the frozen bottle it can damage their delicate bodies.

Now ... I was born with a large dollop of common sense and so to my mind the frozen bottle of water seems a good idea. Provided you leave the heater switched on should the tank water drop below it's set thermostat it will switch on therefore stopping any chance of wild swings the other way. If my tank heats up too far again today I am thinking about trying the frozen bottle idea and because I'm paranoid I'll be dechlorinating the water inside it before freezing!

Amongst my cories I have one of the most delicate species - the panda cory. From experience I know that if anything is wrong with the tank in any small way it's the panda's that keel over first. These high temps will be making them suffer. I also have peppered cories and I know they prefer a temp of 24 degrees - again a cool water cory. I know very little about my melini cories but I do know they are closely related to the panda and so I'm classing them the same as them. I also have bronzes but I think (and please correct me if I'm wrong) that they are one of the cory species that can handle it a little warmer.

I'm really concerned that I'm going to start losing panda cories and that will really upset me as they are my favourites. I've just dropped in some food as the panda's were all hiding - I wanted to see if they'd come out and eat and they have so they must be coping.
The tank light is going back out shortly for the rest of the day. My plants will have to suffer for the sake of my fish

They are saying that the frozen bottle can have the tank swinging wildly the other way causing stress to the fish and potentially causing white spot.

That's why I said...

If using this approach, you need to be dedicated & persistent if you are to avoid causing big swings in the temperature, which as I've already said, can be more harmful than the high temperature itself.

Leaving the heater switched on is sensible, but if the heater is set to 25, and the tank's at 32, that's a 7 degree drop which is still too much if it happens rapidly.
In short, you need to be prepared to get into a regular routine of monitoring the temperature every hour and adding or removing bottles as necessary. If you can't or won't commit to that sort of schedule, it's better to do nothing than risk wild swings in temperature.

They are also saying that if any of the fish swim into the frozen bottle it can damage their delicate bodies.

Whilst I'd agree there's a theoretical risk here, not so much of a fish accidentally bumping in to it, but of something like a pleco latching on to it. However I'd say the risk is no greater than the risk of a fish burning itself on an aquarium heater. It does happen, but only rarely.

Good point about leaving the heater on, it's also a good time to make sure the heater isn't coming on when it's not supposed to. I don't know about anyone else, but in my experience broken heaters (especially if underpowered for the job) can go undiagnosed in cooler temperatures.

I hadn't considered the effect of evaporation. My fish room varies in humidity 56% at present, it goes higher if I spill water on the carpet, on a colder day if I'm cooking 'em it can be as dry as 40% (even with cover glasses off).

I'd be tempted to ride it out, however, if you are set on warming some ice, as the day heats up, your overall aim would be to keep the tank temp stabilized. If a full ice bottle might heat too quickly and cause too much of heat loss of the aquarium water in an uncontrollable way, you could drop say 3 or 4 icecubes into a bottle of cold water (and pop that in the tank), that way you can better regulate the number of ice cubes you heat

Add more ice cubes as necessary on a regular basis, to keep the temp the same.

If my previous post seemed to suggest adding constant fresh cool water was an option, it's not practicable in most cases, it was just a possibility that was mentioned. A bit like: Jim lost his phone in the bar - one possibility is that he did it on purpose, the other possibility is that...

It's so hot, why am I using the dryer when I have a perfectly good washing line!!

at present my tank is about 1 degree above normal which doesn't warrent much action to my mind. Later on last night though it reached 28 which I found 'uncomfortable' ... that was worrying me. I've just spoken to my Dad and his tank is running hotter than normal too. His runs at a similar temp to mine and his is up 2 degrees. He lives in an old stone built cottage that gets very little sun. He's also got thin sheets of polystyrene around his tank from winter when it was really cold - it's clearly not having an effect on keeping it cooler in summer. His tank is old and has a condensation tray and so he's better placed to keep his lid open without worry if finding fish on the carpet! I've told him to open the lid and see if he can get his down. He's got a bachelor group of platies and they really don't like it too warm

My heater is an external Hydor. I can hear it click as it comes on and goes off if there's no other noise in my flat (I can't hear it if the telly is on for instance) I've not heard it come on since Monday so the thermostat on it is obviously okay.

At the moment I'm going to steer clear of frozen water bottles if I can - I guess that might change though if the heat wave continues longer than a few days.

Hmmm... here's a bit of theory...

- 1 ltr of fish tank water at 30 Deg C holds 3,000 cal (of energy)

- 100 ml of ice is able to absorb 800 cal (and thus reduce the temp to 2200 cal per 1.1 lts or 22 Deg C)

Put this in proportion:
- 100 lts of fish tank water at 27 Deg C holds 270,000 cal

- 10 lts of ice is able to absorb 80,000 cal (and thus reduce the temp to (190,000 cal per 110 lts) or 19 Deg C)

But we don't want it that cold (19 Deg C is too cold! and too quick):
We might want to try dropping it by about 1 Deg C...

In which case, my very rough, ill informed, stab in the dark, theoretical research only advice is:

For every 1 ltr of ice placed in a 100 lts of 27 Deg C tank water, should reduce the temperature by about 0.8 Deg C.

So for a 200 ltr tank, you might be looking at 2 x 1ltr pop bottles of solid ice.

And remember... while you're trying to cool the water down, you've got the room temp always working against you to push it back up, in which case, if the tank temp stays the same, you've found the equilibrium and it's a result - If anyone can be bothered to do the practical experiment, let me know the results. I don't have the freezer space at the moment, too much blood worm  

well ... at the moment I've not got any plastic bottles as the recycling took them all away on Monday so I can't try it. Tank is currently at 26.5 ish so not as high as it was at this time yesterday.

We had a massive thunder and lightening storm this afternoon which has dropped the temp outside a little bit and tomorrow is supposed to be cooler anyway. Continue playing it by ear for now

well I've got up this morning and all my fish are looking really sluggish - one of the elderly harlequins isn't looking great and looks like it's in the throws of looming death. I left my windows open all night and closed the living room door in the hope it would cool the room but the tank is still at 26.5 so that didn't work!

I've now added my sponge filter running off my air pump to try and add some extra oxygen for them. Somewhere I have a double valve for the air pump so I can run two sponge filters or two air stones. I also have an air stone somewhere. I need to hunt them out then I can have the sponge filter at one side and the air stone at the other. The fish are picking up slowly and it's only been running about 15 minutes. They must be fed up of the heat now ... I know I am. I've woken up with a banging headache

Always an idea to check water parameters from time to time, just to make sure it's nothing else.

Headache - you're probably dehydrated - plenty of fluids. Check your wee colour, if it's green, there's a problem

cheeky so-n-so

I am keeping hydrated ... but the heat is affecting my Fibromyalgia and arthritis so I've got 'everything ache' today. I'm heading down to p@h soon as I can't find my air stone - I must have chucked it out. I might look at one of the long type one's and add a bubble wall type thing. It'll give the fish something to play in ... the harlequins are enjoying the bubbles from the sponge filter so they'll probably like something like a bubble wall to play in.

I picked up a small bottle of coke at the supermarket - I've emptied the coke into a glass and filled the bottle with water and it's now in the freezer on fast freeze. The tank was 27 degrees again when I got back from the supermarket. I've turned the cooling fan back on and it's come down to 26.3 ... the fan seems to be the best way to cool it down but it's an expensive way!!

I called at the lfs for some frozen blocks of food while I was out and someone was there asking the staff about their tank over heating. They gave the frozen bottle of water advice so it would seem that is the advice for this short term heat wave

I'm not sure what size fan you have, but the one I see on the Argos website is fairly typical 16" blades and 50 watts.

If you pay about 17p per kw (1000 watts) of electricity (typical token meter cost), and run it all day and night long:
50 watts x 24 hours = 1200 watts.

So the cost should only be 17p x 1.2 = an extra 20p per day. Does that sound right?

- whereas, if you had a faulty 300 watt heater stuck in the on position:
300 watts x 24 hours = 7200 watts.

So you'd notice 17p x 7.2 = 1.22 per day.

Just wondering (fans don't usually use much electric) what you've said stands out to me.

the fan I have is from Argos, it's one their own brand tower fans. I guess I was just assuming it would cost a lot to run but from what your saying it probably doesn't. I'm probably worrying over nothing!

We've just had some rain and now the temps outside are dropping. There's the frozen bottle of water in the tank and now the temp is lowering. I'm down to 25.9 which is better. The extra air going in from the sponge filter has perked them up aswell and they're all out having something to eat now. All seems well

I'm sure the savings on heating will compensate a little bit of fan - it's less than six months to Christmas

Yey!  I'm back down to the normal 25 degree's this morning. The elderly harlequin is still looking sickly though, she's lost a lot of her colour and is swimming like she's just exhausted. I have been losing them one after another though so this is no surprise. I think the heat just speeded up the age related process.

The fan is 45 watts so I got my Dad to work it out and it basicly uses about the same power as a light bulb so not much. I was worrying unnecessarily.

All my fish seemed to really like the bubbles from the sponge filter though and so this morning I added the air stone block instead. I got a 6 inch one and I've added it to the back of the tank. The harlequins are investigating it and playing in the bubbles! My cories were going crazy last night too. They were zooming around the tank, my panda's melini's and bronzes were all playing chase with each other ... it was better than watching the telly Gotta love happy fish

it looks like the heatwave has taken it's toll. I've just found a dead female Melini cory and she was new so I can't blame age. The Melini's are related to the panda's and so I'm guessing they won't have been able to cope with temps of nearly 28 degrees. I also had a dead kerri tetra this morning too but he was really old and looked like he'd had some kind of hemorage - there was blood under the skin from head to dorsal so I thought some kind of brain hemorage perhaps?

The elderly harley is still swimming but looking weak and now there's an elderly black neon looking much the same. I am torn between old age, high temps or 'something else' but my angels are fine, my other cories all seem well (one set spawned while I was out yesterday as there's remnant's of eggs on the glass) my new tetra's all seem okay, as do my new young harley's and Mr Curviceps is fine too. If apparently young and healthy fish were getting sick I'd be more concerned but it seems to be all my older stock that are dropping off one by one and so I'm leaning more toward old age related rather than 'something else'

I wish they could tell me though just so I know that they're not sick with something invisable :/

Deans_Angels wrote:Always an idea to check water parameters from time to time, just to make sure it's nothing else.

In particular ph and kh?

well obviously because I'd found a dead fish I checked to see if it had messed up my water and yep ... got a nitrite reading. I've just finished doing a 50% water change.

I have a JBL test kit and won't be replacing it though. I find it too complicated and if you leave the test tubes too long you get a false reading ... I left the test tube for 5 minutes and I got a high reading. I did the water change, re-tested and timed it for the exact 3 minutes and no nitrite. All this means that the first reading probably wasn't as high as I thought and so I've done a large water change for no reason!

My pH is always low (blame the soft Yorkshire water) but stable - until I have to do big water changes!! So now I've probably messed up my pH because I thought I had a higher Nitrite reading than I actually had .... fun and games - NOT. Back to the API kit asap for me.

kH is also low despite crushed coral in the filter.

My main worry is I've got some kind of disease that I'm missing but apart from the cory all the fish I've lost over the last 6 months have been more than 3 years old and so common sense says old age and nothing more .... at least I hope

Yes, the test timings are important.

If you have a modern mobile phone, you can set a timer to bleep after x number of minutes. Works for me, but if you're not familiar with the test kits you're using, you need to read the instructions

I like the api kits because the colour cards have a visual reminder on the back. Which is good for a quick double check (helpful when none of the tests are the same).

You got a bad reading and then a good one. I'd be tempted to test again tomorrow, using a timer to improve accuracy. That way, in good daylight, you can be doubly sure that the first reading was wrong.

I meant to re-test first thing before feeding but forgot. They're all out and eating now so I'll leave it till this afternoon. I know from experience that you can also get a false reading if you test during or shortly after adding food.

I ended up having a mostly sleepless night cos carrying 20 buckets of water did my back in and I paid by not being able to sleep. I'm still in agony now and I'm begging codeine to be my friend. I'm going to have to get sorted with a python water changer ... I keep saying I'm going to buy one but never get around to it!