Sps stopped growing mysteriously - nitrate problem?

[whatnot45]

My Sps went through a rapid growth period recently but in the last couple weeks or so they stopped and the colours started fading. A week ago I did a big water hangs but that didn't help at all. I recently started getting LOTS of those micro feather dusters in my sump like millions of them so I thought maybe they were sucking out calcium so I upped my calcium dosage and that hasn't helped either. I broke out the test kit and my alk, calcium, magnesium, phosphates are all perfectly fine. I also tested nitrate and got a zero reading for the first time ever.

Could that be the reason for the slow bleaching effects? If so how do I safely bump up my nitrates without causing a big algae bloom or something like that? Should I just feed my fish more? I have recently been feeding a lot but nitrates are always zero. There's no mechanical filtration just a very DSB in the sump and a skimmer. I've never had this problem before! Usually I'm battling to keep nitrates low now I can't keep them up.

 

[Tweaked]

Less food in the column could very well be the issue. Or a dozen other problems, but not sure without more info. How many fish do you have, what size tank, lighting, flow, etc.

 

[reefmutt]

And how old is your system? Maybe the dsb only just became fully active?..
What is your p reading?
There is often a correlation between dropping n and a reduction in color and growth..
Do you add any coral foods like reef chili or reef roids or phytoplankton?
Or aminos? Maybe something like this would help..
There is also the option of actually adding nitrate to the system but this requires close attention..

 

[whatnot45]

The phosphates haven't been tested in a while but I use RO DI water and I've tested in the past several times and it's always been zero.

The tank including sump is about 90 gallons I have a juvanile blue tang and yellow tang (don't worry the LFS will buy them back when they get big) a clownfish 2 gobies and a bi color basslet.

I have a flame scallop that I target feed phyto about once a week and it's been alive and well for 5 months now I also have a photosynthetic purple gorgonian which is doing just fine.

I have 2 reef radiance dm 165p+ lights and about 4,500 gph of wave action flow from 2 jebao 40s and another 500 gph from my sump return pump.

The tank is about 9 months old and the DSB in the sump is about 9 inches deep but it's not that big area wise.

 

[Cosmojo]

how much/often do you feed, and of what? system sounds too clean if you legit have 0 nitrate

 

[whatnot45]

I feed frozen mysis 4 times a week and nori 2x and usually have 1 skip day
Also a small amount of phyto once or twice a week targeted at my flame scallop