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Hi there,

My 75G tank has been set up for 6 months now. PH has been dropping steadily from 7 (reading from tap water) down to 6. There's approximately 15 lbs of DW in this tank. I do 25% water change weekly.

Last Sunday, I got a set of KH / GH test kit. Readings after water change as follow:
KH = 2
GH = 5
PH = 6

All fishes (Angels, CL, Congo Tetra, SAE) are doing well. Should I do something about the low KH? If so, how could I raise it safely without changing the PH dramatically? Thanks.

I would add some plain baking soda to your water change buckets until the kh equals at least 3. If you still have ph problems you can raise it up to 5. Do small 10% water changes with the baking soda added to slowly raise the tank kh. I'm not sure the exact amount of baking soda since I have the opposite problem with my water but it should only take a fraction of a teaspoon. I know there's a formula for it online somewhere.

Hi,
The Carbonate Hardness (KH) is a measure of the water's
ability to buffer and with a KH of 2 the driftwood is
probably overwhelming it. As Sham suggests, raise the
KH to a 3 or 4 and hold it there useing baking soda.

A teaspoon in a 75 gallon tank will not make all that
difference. It will probably take a couple of them to
bring the KH up to a 4.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

I found this "recipe" onine:
http://cichlid-forum.com/articles/buffer_recipe.php

But I also remembered reading somewhere that baking soda will drive the PH upto 8.2. Ideally, I'd like to maintain the PH of this tank at 6.5 - 6.8. I'll experiment a bit with the water drained from this tank in a 10G tank to get the right amount of baking soda added.
Thanks.

Hi,
Actually, the baking soda will buffer the tannic acids
being released by the driftwood, and any organic acids
from the fish waste.

Yes, if you add baking soda, the pH will rise, but you
can control it by watching how much you add.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

I was thinking per a 10% water change not the amount you'd need for the whole tank. For the whole tank then yea you'd need a few teaspoons to raise it.

If you add enough baking soda you could make it to 8.2. If you add a small amount of baking soda you'll only get a small kh and ph raise. I suggested baking soda exactly for the reason that it's controllable unlike say limestone or crushed coral. It won't suddenly bring the ph all the way to 8.2 unless you dump a whole bunch in. You just have to watch the kh and test it frequently. If it gets too high the ph will raise and if it gets too low like it is now the tannic acid will cause it to drop. Keeping it between 3-5 dkh should keep your ph around 7. You'll have to experiment on the exact amount needed.

Good stuff
I used to have the opposit problem. The ph of my 32G tank is too high (thanks to the geo system gravel ). No matter what I do, it always drives the ph back up to 7.8 range.

Now at least I have the control to raise the ph of 75G to the desired level.

My be I should just mix the water of my two tanks ... just kidding