Vodka dosing

[rishma]

I think you are observing (at least) two phenomena:

1. When something consumes phosphate it shifts the equilibrium between bound and freely dissolved phosphorus. This means a fraction of the consumed phosphate will slowly leech back into the water through the rock and substrate making phosphate assimilation look inefficient. This can also occur when performing water changes.
2. The carbon, nitrogen, and phosphorus (C:N:P) assimilation ratio is always skewed towards N, and especially C. This means you need a lot of carbon and nitrogen to get rid of a tiny bit of phosphorus.
   I assume after providing carbon you are running into a nitrogen limitation and therefore adding a nitrogen source (especially ammonia directly) helps. Even if you still have moderate nitrate readings it might take time to reduce NO₃ back to NH₃/NH₄ to actually get to the needed nitrogen. I believe this reduction process requires nitrate reductase, and nitrite reductase enzymes, which are based on molybdenum, and iron or copper, if I remember correctly. This makes trace elements another potential limiting factor.
   Long story short: Assimilation of phosphate based on bacteria growth will always be x times slower than nitrogen assimilation (depending on the C:N:P uptake ratio of the participating bacteria species).

Yes. I think that’s about right. Trace is definitely part of it. The actual trace involved I’m unsure about; however, Tropic marin NP Bacto balance includes K+ trace solution. It has iron and copper. No moly.