I would love the help!!!! :beer:
I run GAC on occasion, but not often. I do run GFO because I have some macro algae that grows in my tank. It grows very slowly and is normal a gray color, which I suspect is from the nutrient deficiency. One type is Halimeda, which I know is Calcareous. The others I haven't identified.
Tank Parameters:
- Temperature - 79.9 - 80.3 (Apex Controlled - Probe calibration verified with Calibrated NIST traceable thermometer)
- pH = 7.9 - 8.2 (Calibrated with Fisher Scientific Buffer after cleaning with KCl)
- Magnesium - 1322ppm (ICP)
- Calcium - 445ppm (Red Sea Pro) / 438ppm (ICP)
- Alkalinity - 7.78 dKh (Hanna Checker)
- Nitrate - 0ppm (Red Sea Pro)
- Phosphate - 0ppm (Hanna Checker)
- Salinity - 1.025 (Calibrated Refractometer)
The only reason I'm steering away from the issue being light, is that it was happening with my T5 fixture too. I actually haven't added any coral since purchasing the fixture 12/2 because I want to get the bleaching resolved before buying more coral.
All of those parameters look good. Maybe it's not light. Rocks look very clean;any coraline?Any grazers?
Setting lighting aside ,I've seen corals look like those in your pictures after a rapid drop in PO4 to zero . I have never favored the double zero goals of the so called ulns systems. Corals need some ortho phosphate and dissolved nitrogen and look more vibrant when it's available,ime. it doesn't need to be much but a little consistently available to them makes a difference.
If it were my tank I would put the macro algae control via nutrient limitation objective in second place right now.
It's seems the type of algae you are targeting is not easily limited by low PO4 given the 0 readings . Algae species do vary in terms of the limiting effects of low PO4 with many types doing well with lower PO4 than others. Some may need less, some may cleave organic phosphate and some PO4 may leach from rock and substrate.None can live without phosphate including teh symbiotic algae in corals.
So, continuing to bang at the PO4 even though it tests zero for the water column (even given the imperfections of hobby grade tests and the presence of some algae)may be more limiting to the zooxanthellae and some of the coral's life functions than it is to the particular nuisance algae you are trying to eliminate.
Consider persistently pulling it out and/ or find something to eat it.
I'd feed the tank a bit more,perhaps use a little ammino acid and discontinue gfo for a while allowing PO4 to go to the .02 to .04ppm range.
Dosing a bit of sodium nitrate or potassium nitrate if K is low would be ok. You not going to dose enough K to make much difference in the total in the tank though since I would not dose beyond 1ppm NO3 for the tank and some K will come out with bacterial export.There is no good reason to dose more than that that I can see. In fact, dosing nitrate may not be needed at all if you get enough dissolved nitrogen from foods or aminos.
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