How to accurately dose Trisodium Phosphate.

[DivingTheWorld]

My SPS tank has been consuming Phosphate lately so I've been looking into alternatives to raise it back up a little.

Background:

I was generally running about 0.01 - 0.03 ppm as tested by a Hanna Ultra Low Phosphorus tester. I ran a small amount of GFO in a reactor to keep it low. About a month ago, I noticed it going lower and actually zero out for a couple weeks (0.00 ppm). My sps did not like it and I started getting burned tips, ugly Montis and some acro STN.

When I started noticing these issues I removed my GFO and started feeding more. By doing this I got my readings up to barely something (0.0031 ppm). I did a water change this past Saturday and that bumped me up to 0.0123 ppm (tested Sun), but by this morning (Tues) it had dropped back down to 0.0031 ppm.

I have a bunch of fish in my 80g (89g system volume) tank, and I can't really add more at this point. I feed them as much as they will eat, but I don't want to just dump in food that isn't eaten. So...this leads me to dosing Phosphate. I occasionally dose Potassium Nitrate, so I'm familiar with dosing, but the calculation for Nitrate is fairly simple.

Fish list since this will likely come up as a question:

2 Green Chromis
2 Picasso Clownfish
1 Barlett's Anthias
4 Lyretail Anthias
1 Lamarck's Angel
1 Blue Tang
1 Black Cap Basslet
1 Bangaii Cardinal

I bought a bottle of NeoPhos, but I can already tell that based on the instructions it won't last long. I'm looking for a cheaper long term solution.

Plan:

My plan for Phosphate will be the same as Nitrate. I will make up a solution in a 500ml container, then dose the tank periodically (not more than 0.01 ppm/day) to try to get my phosphates up to at least 0.03 ppm. My target will be 0.02 - 0.04 ppm. My acros and sps have done well at this level in the past.

I think I have read every post on this site concerning Phosphate dosing (and several other sites). The one thing that seems limited is how much to actually dose and what the formula is. It seems the consensus is to dose Trisodium Phosphate, so here is what I bought:

https://www.amazon.com/gp/product/B0...0?ie=UTF8&th=1

If the link doesn't work, it's food grade Trisodium Phosphate, anhydrous, 99.9% ultra pure.

The Planted Tank has a calculator which you can use for Potassium Phosphate:

http://www.theplantedtank.co.uk/calculator.htm (Potassium Phosphate)

1/2 teaspoon to 500ml, 1ml of solution will raise 89g, 0.01 Phosphate

But, since this is Trisodium Phosphate, I tried to find a correct formula specific to that additive. I'm gleaned the following from a Randy Holmes-Farley post from an "unnamed site":

1. add 1.88g of the Trisodium Phosphate to 1 liter of water,
2. Adding 1 ml per 100 L of tank water will boost phosphate by 0.01 ppm

Based on this, my understanding would be:

1. Add 3.1678g of Trisodium Phosphate to 500ml of water
2. Adding 1ml per 337 L (89g) of tank water will boost phosphate by 0.01 ppm

Questions:

How does that look? Does that appear to be the correct formula? I had hoped to figure out a calculation where I could say add a teaspoon to my 500ml container and dose based on that. Trying to figure out a way to weigh 3.1678g of something seems like a difficult task! Any suggestions to make this easier?

[bertoni]

I think my rule of thumb was:

15 mg/gallon of trisodium phosphate yields about 1 ppm phosphate.

Assuming you have the hydrated form, TSP is abut 25% phosphate by weight, so 1 ppm phosphate = 1 mg/L = 3.8 mg per gallon phosphate, multiplied by 4 to give weight in TSP, is about 15.2 mg/L. That's my math.

Do you know whether you have a hydrated or anhydrous form? It's not a huge difference, but it'd be good to know. What level of dosing are you targeting, and what's your water volume? I'm guess 337L for the tank? Your numbers look fine to me.

[DivingTheWorld]

Originally Posted by bertoni

I think my rule of thumb was:



Assuming you have the hydrated form, TSP is abut 25% phosphate by weight, so 1 ppm phosphate = 1 mg/L = 3.8 mg per gallon phosphate, multiplied by 4 to give weight in TSP, is about 15.2 mg/L. That's my math.

Do you know whether you have a hydrated or anhydrous form? It's not a huge difference, but it'd be good to know. What level of dosing are you targeting, and what's your water volume? I'm guess 337L for the tank? Your numbers look fine to me.

It's anhydrous. I have a link in the first post if you want to see exactly what I bought. Tank system volume is approx. 89g (337L).

[Dan_P]

You could go ahead with using a teaspoon to measure the phosphate and make up a stock solution. Then add what you estimate to be the correct amount of the stock solution for raising the PO4 level in a one gallon sample of tank water. If the amount is too small for your syringe, add more than what you estimated but keep track of the actual amount. Measue the PO4 level in the 1 gallon sample.

This is a bit empirical, but it will build your confidence. You are probably worrying a bit too much :-)

[DivingTheWorld]

Originally Posted by Dan_P

You are probably worrying a bit too much :-)

Highly likely!

[bertoni]

I'd give your numbers a shot, and testing the dosage on a 1 gallon sample seems like a good idea, too.