Phosphate dosing and mixing it with Calcium Nitrate

Jason Coy · Apr 17, 2026

I'm creating a 20G long macro display tank that will house primarily macros, including calcified macros, a tube anemone, and possibly some soft corals, mushrooms, zoas, and RFAs. I currently only have macros, mostly red, 1 tube anemone, 1 soft coral, and a 3-3.5" medium bodied lionfish, temporary home. Phosphate with Hannah checker was 0 and api kit showed 0 nitrates. I added a gallon of tap water to the Ato to make about 4.5-5 gallons. I thought that would add some nitrate and phosphate until I could buy and make my own solution. That didn't work out too well as the next day I had a bloom of dinos and nitrate still showed 0 and phosphate checked .15ppm. I threw away that water and switched to ro/di for top off.

I bought some calcium nitrate and bought some sodium tripolyphosphate, thought I ordered the correct stuff but guess I didn't, but had some questions. I tried reading and saw that purity could be an issue for both the calcium nitrate and the phosphate I bought and was suggested not to use but wanted to confirm.

For the calcium nitrate my understanding was that it could probably be used and that the ammonia shouldn't be an issue at 1% as it could be the generally preferred form of nitrogen for macros. Since nitrate was 0 and I was unsure of whether or not to use this I bought some Neonitro and as of right now nitrates are 10 with a Hannah checker.

For the phosphate I was unsure if what I have could be used or not. From what I have read the brand has been suggested for other compounds so not sure about this form. Since I'm unsure about what I bought I have since bought monopotassium phosphate to dose but won't be here until next Friday and bought some neophos since it will be here tomorrow. Phosphate is currently 0 are dinos are starting to come back.

I'm wondering if the calcium nitrate is safe to use and if the phosphate I have can be safely used? Also can both be mixed together in the same dosing container?

Thanks for any and all advice.

Randy Holmes-Farley · Apr 17, 2026

I do not recommend tripolyphosphate. It is three phosphates
Linked together. It likely eventually breaks down to normal phosphate (orthophosphate), but it is not what most organisms use, and its detectability by kit is questionable.

As to mixing, one cannot mix calcium and phosphate is dosing solutions.

Jason Coy · Apr 17, 2026

Randy Holmes-Farley said:
I do not recommend tripolyphosphate. It is three phosphates
Linked together. It likely eventually breaks down to normal phosphate (orthophosphate), but it is not what most organisms use, and its detectability by kit is questionable.

As to mixing, one cannot mix calcium and phosphate is dosing solutions.

Thanks Randy I'll return the sodium tripolyphosphate and wait for the potassium phosphate to come in, using neophos in the short term.

Do you think the calcium nitrate I bought would more than likely be ok to use? I will also keep them in separate containers

Randy Holmes-Farley · Apr 17, 2026

I’m not sure what greenhouse grade means (if anything) but it may be ok. Food grade sodium nitrate is a good choice.

Jason Coy · Apr 17, 2026

Thanks, that's what I kind of figured. I'll get the sodium nitrate. What I have is cheaper but it isn't worth saving money up front if it causes problems down the road. Maybe I'll keep what I have as well and experiment in another tank where it is only macros and nothing else.

If I understand it correctly sodium nitrate and mono potassium phosphate can be added together in the same container as it was the calcium in the calcium nitrate that caused an unwanted reaction when mixed?

Honestly I'm not sure there is anything to be gained by combining them other than having less dosing containers as they are likely to have different demands that would require different doses anyways or is there a formula to figure that out?