I agree this sounds like a starvation issue, which excess lighting will only exacerbate. The fact that things get worse after a WC supports this guess.
PO4 is not too low, therefore low NO3 seems logical. How are you achieving denitrification and is it something that you can decrease the efficiency of? How well is your tank stocked?
I am having a similar issue (well, kinda the opposite really: my acro tissue looks great, no RTN/STN, but I haven't had any PE in weeks). My parameters are very similar to yours and I also dose amino acids and run carbon all the time, but I dose Acro-Power instead of RS. The backstory is I was getting an algae bloom, tested the water and found NO3 at 2 ppm and PO4 at 0.21. So I added some GFO to knock down PO4, and that is when I stopped getting PE from my acro. Therefore I assumed there was a correlation between adding GFO and closed acro polyps. After 2 weeks my PO4 had dropped to 0.03 so I removed the GFO, intentionally removing all of it in order to see if PE would return as PO4 started to rise again.
Well, PO4 has started to rise again, up to 0.13, and still no acro PE. Meanwhile, however, I just noticed this weekend that NO3 has gone from 2ppm a few weeks ago to 0 ppm now. Therefore I'm thinking it was the NO3 dropping to undetectable levels, not the PO4 dropping to accepted levels via GFO, that caused my acro to close up.
As a result, yesterday I opened up the valve on my denitrator to decrease it's efficiency. It will take a day or two for the effluent to contain any NO3, keeping my fingers crossed I can get some PE once I get an NO3 reading above 0.
My point is, I'm having a similar issue as you and my best current guess is it's related to undetectable NO3 levels. One thing that is different is that I've been acclimating some new frags and so I've been running my lights at less than half their normal intensity, perhaps that is why my acro is not declining as quickly as yours...
PO4 is not too low, therefore low NO3 seems logical. How are you achieving denitrification and is it something that you can decrease the efficiency of? How well is your tank stocked?
I am having a similar issue (well, kinda the opposite really: my acro tissue looks great, no RTN/STN, but I haven't had any PE in weeks). My parameters are very similar to yours and I also dose amino acids and run carbon all the time, but I dose Acro-Power instead of RS. The backstory is I was getting an algae bloom, tested the water and found NO3 at 2 ppm and PO4 at 0.21. So I added some GFO to knock down PO4, and that is when I stopped getting PE from my acro. Therefore I assumed there was a correlation between adding GFO and closed acro polyps. After 2 weeks my PO4 had dropped to 0.03 so I removed the GFO, intentionally removing all of it in order to see if PE would return as PO4 started to rise again.
Well, PO4 has started to rise again, up to 0.13, and still no acro PE. Meanwhile, however, I just noticed this weekend that NO3 has gone from 2ppm a few weeks ago to 0 ppm now. Therefore I'm thinking it was the NO3 dropping to undetectable levels, not the PO4 dropping to accepted levels via GFO, that caused my acro to close up.
As a result, yesterday I opened up the valve on my denitrator to decrease it's efficiency. It will take a day or two for the effluent to contain any NO3, keeping my fingers crossed I can get some PE once I get an NO3 reading above 0.
My point is, I'm having a similar issue as you and my best current guess is it's related to undetectable NO3 levels. One thing that is different is that I've been acclimating some new frags and so I've been running my lights at less than half their normal intensity, perhaps that is why my acro is not declining as quickly as yours...