Corals dying slowly HELP

[Eagle aquatics315]

Hello everyone been a while since I have posted because everything has been fine up until the last 2 months. I have a 125 gallon mixed reef tank (1 year old) and I cannot for the life of me figure out why my corals are dying slowly, it is also a low nutrient tank. ALL of my parameters are were I like them and are posted below, they have not changed in months, I have SPS LPS and softies and most of them are either dying slowly or fading out. I have lost almost all of my SPS and some of my LPS like frogspawn, chalices and candy cane corals are slowly receding. ALL of my fish are totally fine and I have none that target coral and my inverts are also totally fine. I have not touched the lighting in a year, I run kessils and a zetlight 6500. Coraline is growing good and I use RODI water also and it reads 0TDS. I have well water also so there couldn't be chlorine escaping through the filter I don't think. I do have an infestation of red planaria flatworms in my refugium but I have never seen any in the tank and have dipped corals and nothing has come off of them, I also use Red sea blue bucket salt and do a 25 gallon water change every 2 weeks. I cant figure this out and it has me extremely frustrated!! IF anyone has any ideas please let me know THANKS!!
Parameters:
Temperature: 79F
Salinity: 1.025 (refractometer)
Phosphate: 0ppm (Hanna checker ppm)
Nitrate: 5-10ppm (salifert)
Alkalinity: 9.0 (Hanna checker)
Calcium: 425 (salifert)
Magnesium: 1320 (aquaforest)
pH: 7.7 (salifert)
Ammonia: 0
Nitrite: 0
RO water reads 0 tds but that's the only other thing I question?? No nutrients in it but can there be other things that can leach past the filters?

 

[tehmadreefer]

Lack of po4 is the problem...

 

[Eagle aquatics315]

Lack of po4 is the problem...

What is the best range to be in?

 

[Cameron A]

I like to keep it a little above 0 like .08 but it has to be something else if you’ve ran these parameters for a year now and had no prior issues.

 

[ScottB]

If my Hanna were reading 0, everything in my tank would be fading. Each tank is different -- and each tank is different a bit through time. More corals (PO4 consumers) over time or less corals over time? More diverse bacteria over time or less? Bioload more or less over time? Has your NO3 crept up at all over time?

What is/has been your nutrient export routine/equipment? Include GFO?

Absolute 0 on PO4 and -- IMO -- only your fish would be alive. No algae, no zoox, no coral.

So as an example, earlier your actual PO4 was .004 (rounds to 0) and rapidly consumed. Now because of growth (coral or bacteria) your actual PO4 is .002. So stuff needs to slowly die off until the survivors can sustain themselves at the new trace level.

I ran detectable NO3 & PO4 for years and did OK. Not super fast growth; not the richest of colors, but fine. Zero nuisance algae. Somewhere along the way I hit 0/0 in my frag system (vacation, not harvesting cheato, general stupidity, etc) and ostreopsis dinos took over. Never again.

Your nitrates are fine, but I would strongly recommend targeting PO4 to .03 at least, .10 at most. But SLOWLY!

Your answers to my early questions determine which levers might be best to gradually adjust. If you are running GFO reactor, that is the easiest and purest tool. Reduce the running cycle from N number of hours to N X .8 for a week. Measure. Reduce again as necessary. I run mine on APEX, but a $20 IoT smart plug will do nicely.

I would not recommend pulling a bunch of levers at the same time. You got to this point slowly without significant mortality. You should exit this position with similar pace.

 

[LesPoissons]

Do you ever feed the corals or add phyto? You could try that. Just sounds like a gradual starvation in a low nutrient system to me?

 

[Retro Reefer]

Check for any possible rusting components in your system.. I had a similar issue on a tank that was doing great, everything declined over several months and nothing I did seemed help. I eventually found a rusted magnet and once it was removed the tank bounced back quickly.. I did a couple large water changes and ran a poly bio marine poly filter for a couple weeks to help remove contaminants after finding the magnet.

 

[FugeTown]

I dose this for phosphate just dose slow cause high phosphate can be even worse than none at all, make sure your po4 test kit is a good one.good luck.