low PO4 and Nitrate

MnFish1 · Sep 19, 2017

Randy,

Lets say you start with a bare tank and cycle it. Add something alive. After a while, Nitrate and PO4 will increase. Either you have to remove it (filtration) or something will consume it in the tank and grow (algae). Once steady state is reached, the levels in the water will show very low Nitrate and PO4 as whatever is being used to remove them or whatever is using them will do so.

So - If the Nitrate or PO4 is higher than recommended that would suggest a problem that is 'fixable' ie more export or less input. But on the low end It could be coral or biopellets (etc) bringing the levels down to 'low' levels or bad things (algae) bringing those levels too low. Do we chase our tail trying to dose these things? (Or am I misunderstanding the concept)

bif24701 · Sep 20, 2017

MnFish1 said:
Randy,

Lets say you start with a bare tank and cycle it. Add something alive. After a while, Nitrate and PO4 will increase. Either you have to remove it (filtration) or something will consume it in the tank and grow (algae). Once steady state is reached, the levels in the water will show very low Nitrate and PO4 as whatever is being used to remove them or whatever is using them will do so.

So - If the Nitrate or PO4 is higher than recommended that would suggest a problem that is 'fixable' ie more export or less input. But on the low end It could be coral or biopellets (etc) bringing the levels down to 'low' levels or bad things (algae) bringing those levels too low. Do we chase our tail trying to dose these things? (Or am I misunderstanding the concept)

The main reasons to reduce and remove NO3 and PO4 is algae control. Some systems after time may not have much of an algae problems though there are NO3 and PO4.

When starting a system you want lower numbers because there will almost always be a large algae bloom at some point in the maturing process. You only need enough NO3 and PO4 to support the corals and a lot depends on lighting intensity, ALK, growth rates, available foods, and more. You have to find your own sweet spot that keeps algae from taking over yet corals do well. In the beginning this can be hard due to various blooms coming and going. You have to learn your own system here and just observe and monitor.

MnFish1 · Sep 20, 2017

bif24701 said:
The main reasons to reduce and remove NO3 and PO4 is algae control. Some systems after time may not have much of an algae problems though there are NO3 and PO4.

When starting a system you want lower numbers because there will almost always be a large algae bloom at some point in the maturing process. You only need enough NO3 and PO4 to support the corals and a lot depends on lighting intensity, ALK, growth rates, available foods, and more. You have to find your own sweet spot that keeps algae from taking over yet corals do well. In the beginning this can be hard due to various blooms coming and going. You have to learn your own system here and just observe and monitor.

Sorry you missed my point. I know 'why' NO3 and PO4 should be removed. I was also using the starting of a tank as an example it wasn't a question about cycling (sorry it wasn't clear). Just so it is clear:

1. When the amount of Nitrate and PO4 consuming 'stuff' in the tank has grown to the point where it is at steady state with the amount of nitrate and PO4 produced by the fish/corals, etc in the tank, won't the NO3 and PO4 always be close to zero? And If so, a low PO4 and NO3 would not be 'diagnostic/prognostic' of a 'good' reef tank. In other words you can have a tank full of algae with 0 nitrate and 0 phosphate.
2. Conversely, a High NO3/PO4 would be prognostic/diagnositic of an unstable 'bad' reef tank.
3. Does trying to dose Potassium nitrate result in merely chasing one's tail or do you (Randy) think that the dosing of varying amounts of nitrate vs PO4 will preferentially lead to coral utilization vs. algae utilization.

Randy Holmes-Farley · Sep 20, 2017

Yes, there are times when it wouldn't make sense to dose certain nutrients and use certain export methods (say, phosphate and GFO), but other export methods have more advantages than just lowering nutrients (say, organic carbon dosing and the potential for the bacteria to feed filter feeders). So in that sort of situation, dosing can make sense.

Moreover, most people that dose either have

1. An imbalance of nutrients (say, elevated phosphate and low nitrate) so that balanced export (say, macroalgae) cannot appropriately bring the elevated one down, and so dosing the low one can actually bring the other in line and maintain appropriate levels of the low one

or

2. One or both nutrients are excessively low and they are not using an export method that is well suited to easy "control" to allow them to rise.

bif24701 · Sep 20, 2017

I find that my system requires additional NO3 and I use PNO3. I keep my PO4 in check with GFO as needed. Adding some NO3 also does help lower PO4 so that I'm not changing GFO every week.

I'm not sure why Ive got so much more PO4 going into my system or NO3 is processed so well. Could be the three MarinePure blocks I have and large Pukani rocks but as long as I keep an eye on them and keep the balance haven't had problems with either my corals or algae.

I harvest almost a bucket full every 1-2 weeks, a lot of chaeto!