Sorry I think I have mislead you all the tank/rain water comment should have been rain water tank I will test again tonight fresh out the rain water tank and my fish tank, I had the opaque storage bottles of water in the sun
you could also try adjusting your lighting also, try to reduce the amount of time your lights stay on for. That can help also. If you have plants that con tolerate low light conditions, even better because you can reduce the light output.