High phosphates and cyano and algae issues

cmackbrown1995 · May 5, 2026

So I’ve been battling some issues for a few months now and I need so help. I’ll start with my set up 140 gal tank with a sump reefmat 1200 and a octo skimmer. Dosing afr a very small amount daily and a ato. with a Magnificent Fox face, 2 storm clowns, and a dwarf flame back angel. 1 holy grail torch and 1 joker torch, bubble algae, gsp, Duncan, Monty, Xenia. And a few mushrooms. I started this tank about 6 months ago. I had several more fish in it, copper band, royal gramma, helfriechi firefish and a six line. Everything was very stable and all of the sudden everything just started dropping like flies. It started with a horrible cyano outbreak and we ended up doing a blackout that fixed that. And it was followed but a horrible green hair algae outbreak. Phosphates jumped up super high and we used phosfiltrum and the algae went away slowly but now the cyano is spiking back up. I haven’t done anything to the tank or added anything in months but I lost over half my fish and the cyano is coming back and that’s when I lost all my fish the first time. Almost all the nutrients are stable except phosphates which are hanging around .35. Nitrates hang around 10-15, nitrates are 0 and ammonia are 0. Mag is a little higher around 1400 and calc 440 and alk 10. Temp is stable with INKBIRD at 79. Salinity is always right at 1.026. All parameters are very consistent every time I test. I use Hanna master test kit for most but if numbers are off I recheck with salifert and seachem. We can’t get the phosphate down. I do tend to feed heavy but nitrates are always good. I’m most concerned about the cyano now and losing more fish. Been battling this cyano/algae/phosphates for about 2 months now if not longer. Corals all seem to be happy and fully extended except when the cyano got on them the first time. I do biweekly water changes of about 25-30 gal. The photos are from the first wave of diatoms/cyano. The new wave of it is not as bad yet. ICP test was fairly normal nothing huge standing out