Marko,

What is the pH of your incoming water? This is important to know in determining how the overall system pH will be once your fish start to grow out. The bacteria need a high pH in order to function at their best. A pH of 7.5 is a good number. Your pH will fall once the fish start to grow out. It is important to make sure that the media in your grow beds does not keep your pH too high. 8.0 is probably the upper limit when your system is new.

The main problem with a high pH is that you will have to watch your ammonia level very carefully, for if it goes too high it will be toxic to your fish. The plants like a lower pH but most will grow in a higher pH water.

Again, what is the pH of your water coming into your system?

Oliver