Rowa phos calculator?

Notsolostfish · Aug 26, 2026

im a bit confused the rowaphos calculator telling me to put 22tbsp all at once in my reactor? Is that to drop phosphate all at once? My total water volume is 150G im aiming for 0.05 a day. My phosphate at 0.66 PM by hanna currently.

Im asking here before i do a big mistake and take a big hit and tick corals off. Thank you for your help.

Bear22 · Aug 26, 2026

Rhowaphos is potent stuff. I use it.

Personally, I would start with half (or less) the recommended amount and go from there. And just kind of bracket your needs via routine testing.

Randy Holmes-Farley · Aug 26, 2026

I don’t know how that calculator is designed.

EnterName · Aug 26, 2026

It's really weird... This is what it does:

raw = litersAdjusted × (currentPPM − desiredPPM)

ml_recommended = ceil(raw / 12) × 12

So your volume is converted into liters and then multiplied by the difference in ppm you want to reach. This makes sense so far because "raw" is now the total amount of Phosphate in the system you want to get rid of in mg (ppm → mg/L).

Then it gets weird:
It rounds the raw phosphate-removal amount up to the nearest multiple of 12. This is the result.
Apparently each mg Phosphate requires 12mL of Rowaphos to be bound.

Then it converts it to oz and tbsp:

oz = ml_recommended × 0.035274 (grams→oz)

tbsp = ceil(ml_recommended × 0.067628) (≈ 1 tbsp per 14.79 ml)

There is no function that makes sure you decrease the amount slowly so I can't recommend following the calculator blindly when you want to get rid of a lot of Phosphate.
The "litersAdjusted" are halved for freshwater btw. Otherwise, it's just the amount you entered converted to liters.

Notsolostfish · Aug 26, 2026

EnterName said:
It's really weird... This is what it does:

raw = litersAdjusted × (currentPPM − desiredPPM)

minimum = ceil(raw / 12)

ml_recommended = minimum × 12

So your volume is converted into liters and then multiplied by the difference in ppm you want to reach. This makes sense so far because "raw" is now the total amount of Phosphate in the system you want to get rid of in mg (ppm → mg/L).

Then it gets weird:
It rounds the raw phosphate-removal amount up to the nearest multiple of 12. This is the result.
Apparently each mg Phosphate requires 12mL of Rowaphos to be bound.

Then it converts it to oz and tbsp:

oz = ml_recommended × 0.035274 (grams→oz)

tbsp = ceil(ml_recommended × 0.067628) (≈ 1 tbsp per 14.79 ml)

There is no function that makes sure you decrease the amount slowly so I can't recommend following the calculator blindly when you want to get rid of a lot of Phosphate.
The "litersAdjusted" are halved for freshwater btw. Otherwise, it's just the amount you entered converted to liters.

I understand. So how many tbsp i start with?

EnterName · Aug 26, 2026

Notsolostfish said:
EnterName said:

It's really weird... This is what it does:

raw = litersAdjusted × (currentPPM − desiredPPM)

minimum = ceil(raw / 12)

ml_recommended = minimum × 12

So your volume is converted into liters and then multiplied by the difference in ppm you want to reach. This makes sense so far because "raw" is now the total amount of Phosphate in the system you want to get rid of in mg (ppm → mg/L).

Then it gets weird:
It rounds the raw phosphate-removal amount up to the nearest multiple of 12. This is the result.
Apparently each mg Phosphate requires 12mL of Rowaphos to be bound.

Then it converts it to oz and tbsp:

oz = ml_recommended × 0.035274 (grams→oz)

tbsp = ceil(ml_recommended × 0.067628) (≈ 1 tbsp per 14.79 ml)

There is no function that makes sure you decrease the amount slowly so I can't recommend following the calculator blindly when you want to get rid of a lot of Phosphate.
The "litersAdjusted" are halved for freshwater btw. Otherwise, it's just the amount you entered converted to liters.

Click to expand...

I understand. So how many tbsp i start with?

Usually phosphate adsorbers have instructions that suggest a maximum amount to add per x gallons. If that's not the case for Rowaphos it's something you would be better off asking Randy than me because I don't know how fast the adsorption will be.