No Nitrate

[KingReef]

My tank has been setup for a couple of months now and I recently ran into an issue. I had an outbreak of the uglies and I think I identified why. My nitrate levels had been holding steady around 10-15 PPM for over a month, then they crashed. I had 0 nitrates. My phosphates were still testing in the .25 PPM range. I don't run a refugium or an algae scrubber. I just run filter floss and a skimmer. There was definitely coralline algae growing and then everything got covered in diatoms. My question is, what would take up all available nitrate? I wasn't doing anything to specifically get rid of it. I have since bought liquid nitrate to dosing and stopped running the skimmer for a couple days. The diatom bloom is gone. I have GHA breaking out, but that should be managed by the CUC. I thought managing nitrate levels was to keep them down...

 

[Ellis Syke]

The algae would consume the nitrates, giving you a false "0" reading. They aren't truly zero, the GHA is just consuming it so it looks like zero.

 

[KingReef]

but the GHA wasn't there when this started. There was virtually no algae visible until the diatoms showed up.

 

[Ellis Syke]

The diatioms started consuming nitrates and then the GHA outbreak began. The way to go about it is to try water changes, check PO4 levels, feed less, and check light schedule. If none of that works to eradicate GHA, then try Fluconozol. That stuff will kill the GHA for sure.

 

[BeejReef]

Tanks do strange things those first several months. I understand the desire to have an answer.
It could be that you have some deep spots in your sand, or lower flow areas in the tank. You could be getting some anaerobic denitrification. People go to great lengths to accomplish this. That's just a theory. It could be any of 1,000 things.

Sounds like a normal step in the tank's maturation, and a fairly positive step regardless. Don't think you're wrong to dose a little N, but wouldn't go crazy either. Keep the gha from becoming a dominant force in the tank w a brush and siphon and, with a little luck, that coraline you referenced will win the race to cover the rocks.