Calculating Nutrient Input

[killer2001]

Would there be a way (in somewhat of a timely manner) to take the amount of food I would typically feed my tank on a daily basis, and quickly dissolve it into a gallon of saltwater so I could record the final NO3/PO4 values.

I was thinking just throw some food into a gallon jug of freshly made saltwater and wait until its dissolved but how would I ever know its fully dissolved, and how long would it take if there's no bacteria in there to consume?

 

[Semisonyx]

Not to any extent that would be useful, in my opinion. You’d be better off tracking nutrient consumption of N and P the way you do for alkalinity and adjust feeding or dosing of nutrients accordingly.

 

[killer2001]

Yeah I can see that, but I was thinking more of, if I can understand the amount of food I'm putting in my tank, how it translates to a final NO3/PO4 value without any consumption. Considering I divide equal exact portions every day. Sort of like a baseline high.

 

[KrisReef]

Some foods list phosphorus, but food needs to go through the fish (or coral) before the final impact to the tank water can be calcualted. The animal may/should absorb nutrients from the food for assimilation that does not appear in waste products to the water. So yes, kind of a complicated question and rotting food in fresh saltwater will provide an answer but I am not certain how helpful those results are comparing them to what happens to food in our reefs.

 

[Randy Holmes-Farley]

I show doing that for phosphate here:

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both

Foods are by far the most important source of phosphate in most aquariums. In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize.

reefs.com

 

[Dan_P]

Would there be a way (in somewhat of a timely manner) to take the amount of food I would typically feed my tank on a daily basis, and quickly dissolve it into a gallon of saltwater so I could record the final NO3/PO4 values.

I was thinking just throw some food into a gallon jug of freshly made saltwater and wait until its dissolved but how would I ever know its fully dissolved, and how long would it take if there's no bacteria in there to consume?

I think @taricha might have looked into something like this. Your questions reflect the difficulties in this approach.

Might be easier to calculate these numbers from the protein and phosphorous content of the food.

 

[taricha]

I think @taricha might have looked into something like this. Your questions reflect the difficulties in this approach.

Might be easier to calculate these numbers from the protein and phosphorous content of the food.

Dan is correct on both counts.
I did some fancy (to me) heated acidic digestions to measure total N, C, and P in my fish flake. Much of this material is organic and won't show on the usual test kits.

This exercise resulted in getting basically the same N and P values that you would conclude from reading the protein and phosphorus levels on the label.
So take the labels as good indicators of the N and P inputs to the system from fish food.