Seachem Ph/Kh Down

Hi Rob,
I think it was on the old forum that you gave some advice on the use of this product.

Would it be possible to recap this as I wouldn't mind some refresher info.

Is this safe to use?
By how many degrees KH do you have to reduce it before the Ph will start to drop?
What does it do to the TDS?

By way of example. My water stats are as follows:
KH = 15
Ph = 7.8

Thanks

I haven't used this specific product, but I'm sure the principle is the same as the Tetra pH/KH minus that I was talking about.....

The key thing to realize is that there is a relationship between, the KH, the amount of CO2 in the water & the pH.
For any given KH the higher the Co2 level, the lower the pH will be.
For any given CO2 level, the lower the kH the lower the pH will be.

A KH of 15 (assuming this is measured in degrees of German hardness) is surprisingly high, and I'd probably get my water double checked before attempting to adjust it.

1 degree of German Hardness = 17.8ppm or 17.8 mg/l so in a 100 litre aquarium 1 degree of German Hardness is equivalent to 1.78g of calcium carbonate.

To take your example: dropping your kH from 15 to 1.5 would cause your pH to fall from 7.8 to 6.8.
Dropping the KH by 13.5 degrees of German Hardness removes 13.5 x 17.8ppm of calcium carbonate from the water ie 240.3ppm and this is how much the TDS (Total Dissolved Solids) would fall.

The important thing to be aware of is that the fall in pH is dependent on the percentage fall in KH, so whilst it required a 13.5 degree fall in KH to drop the pH from 7.8 to 6.8, a fall in the kH from 1.5 to 0.15 would produce a fall in pH from 6.8 to 5.8.

Because kH can fluctuate due to the activity of the bacteria that break down the fish waste, in general maintaining a kH of 2 or above is considered necessary to maintain a stable pH. In practice, lower levels can be maintained provided the aquarist is aware of the dangers and carries out regular water quality checks.

Sudden swings in water quality can cause serious stress to the fish subjected to them, so if you do adjust the water quality for any reason, the important thing is to do so slowly!

Thanks for the reply.

I have used the JBL KH test. According to the instructions, 1 drop = 1*H

Is there a direct link between Kh and Ph in the Higher range?
I appreciate that the Ph tests in particular are not that accurate, but I have heard a few cases on various forums where people with a low KH than mine have a more or less similar Ph?

Assuming you're not using an pH stabilising or adjusting products, from the figures you give you have a CO2 level of 5ppm, an optimum level for plant growth is usually considered to be 15 - 35 ppm, raising your CO2 level to 15ppm, would cause the pH to fall to 7.3. Conversely increasing the aeration and driving off some of the CO2 so the level fell to 2ppm would cause the pH to rise to 8.2.
However with a kH of 15 you need a big change in the kH level to produce a significant swing in pH, dropping the kH by half to 7.5 would only cause the pH to fall by 0.3 to 7.5; conversely doubling the kH to 30 would only increase pH to 8.1.
In short, high kH levels tend to stabalize the pH.