Hi Ricky,
It is very common to have an algae bloom with no detectable nutrients because the algae is taking them up. As far as source, what are you feeding and are you rinsing frozen foods?
Phosphate can also leach out of
LR.
Having battled this pesky problem several times I can say I believe that a combination approach is best. I do water changes, manually extract it. siphon it, run
GFO (in fact I have started running it all the time) and have had a sea hare. The other thing that I put together when the last bloom started was that I had changed to a reef style salt and had stopped dripping
kalk. Well
kalk precipitates out
PO4 and I think that by not using
kalk I set myself up for the algae bloom.
