So, is your assessment that the phosphate is too high?
I'm also thinking the Alk might have something to do with this also. You mentioned that Alk was too high. Do you think the corals were reacting to it in a negative way? Did you plan to have the Alk at 11, if so how long has it been that high. Why bring it back down to 7-8 (which you commented was where you used to have it, how long ago was that?).
Nice questions Oxy. Let me see if I can answer them......
Since I started the SPS tanks (first the 12G and later coral moved to the RSM250), I have always been dealing with "Low Alk" around 7 dkh. For me that wasn't "Low", but membranes from other forums told me several times I need to increase it to at least 8-9 dkh. The bottom line is that I never tried to increase it, just to keep it. Why I never tried ? because corals looks happy at 7 dkh. My Ca at those moments was always around 350-380 ppm.
Well, after 10 months of the SPS in the 12G at those levels of Alk and Ca the coral were relocated to the big tank (RSM250). On this tank, I was able to adjust the Alk at ~8 and sometimes I measured it and was at ~9. Lets say 8-9 dKh. Ca was always at 380 ppm.
I was always using Petco NSW.
I never measured Phosphates. To tell you 100% the true, I do not remember, until now, when was the last time I did a full set of measurements in a tank. Neither when I cycled previous tanks. I just look the changes in the tank and you know where you are in the cycle. Bottom line, I measured phosphates on the RSM250, Ammonia, NO3, etc, when I started to see changes in the corals .
Back to the point...... I started to see small changes. Corals where not so happy. So I decided to buy new Red Sea kits, and I found that the Ca was too low, really low. At that point I was seeing some changes in the corals, but they continue growing. I did a lot of testing using Salifert, Red Sea and API kits to finally decide that my old Red Sea Ca kit has an issue and I trashed it.
I leveled the Ca back to 380-400 ppm and started to fight some STN (you have read those postings). Something has to be wrong. So I got the full set of classical water quality measurements kits. Among those was the API phosphate kit. Suddenly....WOW I discover that phosphates where high. I ordered the Hanna kits for Phosphorus ULR, Alkalinity and Ca. The results of the Phosphorus kit in ppb need to be multiply by 3.066 and divided by 1000 to get Phosphates in ppm. WOW...confirmation of the API kit...Phosphates were high.
Around this time Alk was ~9-10 dkh . Why it was high ? if corals grew significantly since I relocated them and I never changed the dosing rate. Could be the dosing pumps have an issue ? , but I discarded that because I counted the same amount of drops in the time period the pumps were working as months ago.
Started to focus in the Phosphates. Reduced the food to half (every other day), stopped adding coral food (phyto, aminoacids, etc). A couple of weeks passed and nothing, Phosphates still high. But my surprise was that ALK jumped to 11-12 dkh. At this point, almost all the corals had reduced polyp extension and they looked very unhappy. The red planet, that never had a reduction in polyp extension, now polyps were retracted. I also observed a reduction in coral growth
I stopped the dosing pumps. Let the Alk go down to 7-8 dkh and started the dosing pumps yesterday.
One hour ago I measured:
PO4: 0.18 ppm
Alk: 7.6 dKh
Ca: 400 ppm
I can tell you that the Red Planet coral has now (after these 4 days that the Alk was going down slowly) the same polyp extension as before. And other Acros started to extend also the polyps. Not yet as in the good times, but I can see they look happier.
My Hypothesis,
as of today and in lieu of what I am seeing, is this one:
The Phosphates are high. I don't know since when, but there was a point, that I started to see a reduction in growth to an almost stop in many acros. If Phosphates interfere with coral calcification, it make sense that
" High PO4 >> Low Coral growth >> increase in ALK >> coral issues" .
If there is no use of Alk, because coral are not using Calcium Carbonate for the skeletons, I will assume that the alk level will slowly raise in the tank. Dosing pumps are always dosing XX amount, doesn't matter if it was or wasn't used. I am not a Chemist, so I am really not sure if this is true. But make sense to me. In the same way, I also measured a Ca increase.
If I confirm in the following days/weeks that there is a real improvement in the corals
and the PO4 levels do not go down, then I will say, with certainty, that Alk at 11-12 dKh, in my tank conditions, was affecting "coral happiness".
Sorry........answer too long.
Cheers
Daniel
PS; OXY.....
How long was that ? you asked. I will say that all the changes started around August/September but I do not have a precise point of reference to know when the Alk started to increase. I do not measure it each week or every other week. Neither when the PO4 increased, because I never measured it in years in my other tanks. Less in this one, until I saw issues with the corals.
). But, with two types of algae I don't understand why you are having PO4 issues. No need to pull the algae out. But, algae may have been a contributing factor, algae also gives off allelopathic compounds. But you are running carbon now, so you don't have to worry about it.
I hope those recover.
