My system has been running for about 7 months now, it's about 1300 L, / 350 G total with about 60 fish a combination of tilapia and gold fish all between 3" & 6" in size. I'm using one IBC 12" deep filled with broken clay brick as the media, and a second IBC 14" deep with a raft on it. Lots of air stones in different locations throughout and the media bed is constantly flooded.
The system is in my basement and each IBC is under a 400W MH lamp that we run 12hrs + per day.
The issue - my top up water is a PH of 7.2 - my system PH will sit at 7.2 when I don't adjust the PH of the top up water via HCL. Some plants have some brownish spots on them - chard, bok choy. and the chard leaves don't always flatten out / open up, they often stay curled under. This issue seems worse on parts of the raft but does appear to some degree everywhere.
I was thinking (dangerous at the best of times but usually just to myself and my wallet) that based on what I had read maybe it was a calcium issue. I picked up some test strips, and my GH (General Hardness) is off the chart so above 180 but my KH (Carbonate Hardness) is below 40 - again, this is based on some test strips (from what I have read test strips are suspect at the best of times)
In the name of full disclosure, I have added some chelated Iron, some KCL and Mg via epsom salt.
After reading through this thread and others I still don't see any answers on how to address the very low KH and high GH.
I just added filtered tap water. Our water supply in Colorado is mountain run-off and they utility shows it as low to medium hardness. I have topped off a few times. I have also used your pH up kit with Potassium Carbonate and Calcium Carbonate many times to adjust pH. I have a 130 Gallon glass tank with a hydroton filled grow bed and about 30 young tilapia. My KH is very low (~35ppm) and my GH is VERY high (>350ppm).
What else can I do to get KH up and GH down?
The API test kit suggest their water softener pillows but I saw some discussion that made them look dangerous to use and saying they release sodium.
They say they have a carbonate buffer to increase KH but is that any better or worse than using pH up?
I purchased a SenEye aquarium meter which doesn't match at all the pH or Ammonia values I see with an API test kit and they say a low KH may be the problem.
BTW, I spent over 5 months trying to cycle my system until I realized my API Ammonia test solution for Ammonia was reading totally wrong. I had purchased another and finally decided to try it even though they said there was NO WAY their test kit would be wrong. Sure enough it showed my ammonia was long gone! Ugh!