Phosphor dosage?


Lifetime Members
Lifetime Member

I received the data of my tap water from the supplier.
It says in mg/l

Nitrat 45,9
Sulfat 54,53
Chlorid 17,78
Phosphor 0,12
Fluorid 0,1
dH 10,4
Calcium 54,8
Magnesium 11,8
Kalium/Potassium 4,11
Natrium 6,47
Fe 0,008

I used the Nutri-Calc to determine what I need to dose my 112l Tank.
I also use 1/3 RO water
So I divided all numbers by three and then multiplied by two to put in the calc.
My targets were
Nitrate 30
Potassium 30
Phoshate 3
Magnesium 10
Fe 0,5

Can I use the number for Phosphor to calculate the Phosphate?

My Phosphate in the tank seems to be superhigh. Tested with a JBL drop kit,
(I know those kit aren´t accurate, but the kit almost explodes so there has to be at least some Phosphat too much.

The last week I realized algae occuring in all tanks. I did never have algae problems before, have to admit though that the growth since using EI is a lot better.
My Co2 is around 30, I use a drop checker with reference kh4 solution.

I am a bit concerned that I might not read the data above right and put in the wrong numbers and therefore dose too much.
In tsp I dose
1/4 K2SO4
1/16 KH2PO4
1/4 MgSO4
no KNO3
5ml TMG

Today I did water changes in all tanks with 50% and dosed only 1/2 EI.
btw. I diluted all amounts x10 in 500ml RO water and dose 50ml 3xweek and also the TMG on the other 3 days.

I have lots of pearling in my tank, Eusteralis stellata is groing like mad, Rotala green is not so fast, the rest as well is growing good. I prune regularly.

Am I on the right path or am I missing something? I tend to panic and fall back into the old school techniques...

Thanks for any input that might clear things a little.

Tom Barr

Staff member
Jan 23, 2005
I wonder how stable the NO3 is in the tap water.
These can vary with spring and summer and various multiple sources they use for supply.

This can make some issues hard, I had tap that was 1.2 ppm of PO4, then 0.5ppm.

So I add a little more PO4 rather than hoping they would add the higher range.

So if I added for example: 1 ppm extra of PO4 per week, then even if I had 0.5ppm for the tap water, I'd still have 1.5ppm. If the water company sent me 1.2 ppm, then I'd have 2.7 ppm.

This prevented me from going too low with PO4.

The NO3 is more of a problem.

I do not like having higher levels of NO3 if I can avoid it, but......if the PO4/ Mg/Ca/K+/Fe + traces/ and you are pretty sure about CO2, then that only leaves you with one thing.


Now if the plants show signs of low NO3, then you can assume that might be the issue. They will stop growing pretty quick if there is low NO3.

BGA algae, some will get holes in their leaves etc.

If the water is 50% RO, and the tap is 25ppm(or we assume that it is 25ppm), adding KNO3 might resolve this without adding too much NO3.
So try adding KNO3 at 1/4 teaspoon 2x a week. That should not add that much more, so you might have at worst, 30-50ppm range of NO3, which is still not that bad. But at the low end, you will have about 5-20ppm.

So both cases should provide good routines.

I know plants will grow very well, best at about 20-30ppm of NO3, more is not that helpful.
Fish will not see effects of high NO3 unless it's above 80-120ppm for extended peroids, I've yet to see or kill any fish at 160ppm NO3.

Shrimp have died after 3 days at that level, but not fish.

Tom Barr