How much Phosphate in DIY Fish Food?

Nick Rose · Sep 15, 2019

I was wondering how much phosphate would be in DIY fish food but mainly Spirulina. The fish food I made was 1lb shrimp, 1lb scallop, .37lbs of Flying Fish Roe, 2 sheets of nori and Dixie cup of Spirulina. I think I put in too much Spirulina but don't know. I feed 1 cube in the morning and 1 in the evening. The cubes are 1/2"x1/2"x1/2". The reason I ask is that my phosphates have been holding steady below 1ppm(I know thats high). Theres been times that its .5 and the ICP test I had a reading of .16ppm of phosphorus. The tank is a 60gallon system, has several coral, 6 fish, protein skimmer, filter sock, and large ball of chaeto. I dont have any algae outbreak but do have some algae on the glass.

Gareth elliott · Sep 16, 2019

Nick Rose said:
I was wondering how much phosphate would be in DIY fish food but mainly Spirulina. The fish food I made was 1lb shrimp, 1lb scallop, .37lbs of Flying Fish Roe, 2 sheets of nori and Dixie cup of Spirulina. I think I put in too much Spirulina but don't know. I feed 1 cube in the morning and 1 in the evening. The cubes are 1/2"x1/2"x1/2". The reason I ask is that my phosphates have been holding steady below 1ppm(I know thats high). Theres been times that its .5 and the ICP test I had a reading of .16ppm of phosphorus. The tank is a 60gallon system, has several coral, 6 fish, protein skimmer, filter sock, and large ball of chaeto. I dont have any algae outbreak but do have some algae on the glass.

Too many variables to guess the P content in your food. I can say spirulina powder is nutrient dense i use to feed tree frog tadpoles and it does muck the water up quite a bit even using .1mg per dish.

You could test if could standardize a portion and feed to a known volume of water and allow x time for breakdown. Say a 2lt soda bottle with an air line. Add 1 cube test with a hanna checker after some number of days. Just be sure to top off.

Divide by 2 and then multiply by the liters in your tank. Will give a rough idea how much you are adding with each cube.

phosphate binds very well to aragonite, so even if you fed 0 cubes you will not see a depreciable value change for some time.