fish dying (long Post)

[eli@fijireefrock.com]

I will have to agree on this one.
Your ph is way low,so you are creating very high co2 in the evening depleting the oxygen from the tank,killing your fish.
Place an air stone for the evening or have an airline running from the intake of one or more of your power head simply to add lots of oxygen back into your tank.
Do you run a calcium carbonate reactor check for a leek into your tank of co2.
If it's not the case It would simply not enough aeration or agitation of your water surface.

Originally Posted by pinhead

If they are fine during the day but are dead in the morning it is not your water parameters.

I would think that the oxygen levels are too low at night as the Corals and Macroalgae switch from photosynthesis to respiration. During the day they are using Carbon dioxide and producing oyxgen and at night the reverse occurs. The carbon dioxide produced at night is the reason pH also fluctuates between day or night.

Without an easy way to measure oxygen levels, the simple solution is to run an airstone at night or point some extra powerheads at the surface of the water for better gas exchange and into the rocks to prevent areas of low oxygen.

Try these simple solutions before you worry about your water.