Might I make a suggestion or two in the form of a few questions?
Where are you getting your water from? Have you looked at your water under a scope with a Sedgwick-Rafter chamber? I would be curious to see what is colonizing your substratum. I can think of a few obvious culprits like the Cyanobacteria, but I have a couple of other culprits in mind that are a little more rotten. Have you noticed any fish behavior that might suggest a dissolved oxygen crash? This would be particularly noticable in the early morning hours and your DO concentrations would probably be less than 4 mg
. Fish are obviously stressed at 4 mg
/L and fish kills in natural systems are common at O2
levels below 1 mg
/L. The strange thing about this is that it is easily explained. An algal bloom at the right time can cause DO levels to drop dramatically in natural waters. Algae shift to O2
respiration at night acording to a supposed Circadian rhythm. Once the light of day hits, they revert to photosynthesis.
Just my $0.05...was $0.02...****ed inflation...
EDIT: Are you using NSW
as make up water? If so, where are you getting it? Is it oceanic or is it bay/estuarine?