Hi, problems with low nitrates do exist, but I don’t think this is the case.
I don’t know what is causing this and I’ll tag along, but I’ll tell you my experience with nitrates in case it’s of any use.
I was having some bad algae problems and I was trying to starve them to death. I was heavily dosing carbon (in the form of ethanol) and my nitrates read at 0. Nitrates were low even before I started dosing because the algae was consuming all of it. Slowly my corals lose color. I had a brown pocillopora that became ghost white. It looked as it had bleached. After discarding temp and light I started dosing nitrates in the form of potassium nitrate. This brought the color slowly back. Today my pocillopora has a beautiful color and it has spawned with babies all over the tank, it’s a plague and I’m thinking of removing all of it, haha.
I’ve been dosing for over 2 years, and with carbon dosing you can completely control where you want your nitrate and your phosphates.
I’ve changed from potassium nitrate to calcium nitrate because the potassium was accumulating, whereas calcium nitrate adds calcium and alkalinity (if the nitrate is consumed) at an equilibrated rate.
Downsides to this method is increased cyano, and also bacterial mats that grows inside my vectras diminishing their flow. If I turn them off and on some of it comes out. Corals that grab some seems to eat it. Both of this problems are due to the ethanol though, not the nitrates.
Currently I dose 5ml of calcium nitrate 1M and 10ml of 96% ethanol daily. I’ve a 500g reef and feed heavily. I’ve phosphates at 0,01 ppm and nitrates at 1 ppm.
I’ve toyed with nitrates values from 0,1ppm to 10ppm and around 1 is where I like it more.
Good luck!