Hello, this is my first post in these forums, lately I have encountered some problems with my KH in my medium to heavily planted 190l tank. I have a pressurized co2 system with ph controller set to 6.5.

Now normally I dont usually test my water, I do regular water changes of 25% every week. As of lately, I noticed that plants didnt pearl as they did before. After some water testing I found out that my kh is only 1 to 1.5, this leads to a low co2 count.

I have tested the tap water which I use to do my water changes, and the kh is 4.

How can I stabilise the kh of my tank so that I can have a larger amount of dissolved co2 in my tank.

First, you could change more water every week, which would drive the KH back more towards the tap water value. Second, you can add bicarbonate of soda to the tank at every water change to raise the KH.

Tap can vary that much also, but testing the tap and the tank for KH is wise weekly.

If you use pH/KH measurements, do not assume the KH is stable.
If you run low on CO2, the plants will attack the KH as a carbon source as will algae which will compound the problem even further.

I watch the plants, which your were doing. They generally will not pearl much, growth rate slows etc. That's low CO2.

Regards,
Tom Barr

I have bought Bicarbonate of Soda so that I can raise the KH, but if I add it, it will also raise the PH. If I add more co2 to bring the ph down, will the kh decrease too, ending up in a endless cycle?

Last time I had checked the kh of my tank, it was stable at 6dkh and I was running at about 20ppm to 25ppm co2. One thing I have done lately was to double the amount of light I have over the tank, ending up with 152w of light, around 3wpg.

I have took a sample of my tank water, left it 24h to standby, and after I checked the ph, it was at 7.65, dont know if from this you can calculate the co2, but I have read it somewhere in these forums.


Below are the water parameters as of this morning, is it possible that the KH is crashing cause I am reducing the PH so much?

Tap Water Parameters

PH 7..5
KH 6
GH 17

Aquarium Water Parameters

PH 6.5
KH 1
GH 16