Redfield ratio is 1:10 in terms of MASS of PO4 and NO3.
RR is an atomic ratio, atoms, nothing to do with weights of the nutrients!

Folks have misapplied RR for about 20 years in the hobby..........

there is a web site in Dutch that is popular, and unfortunately very wrong that is promoting this RR ratio idea.

While well meaning, it's simply put: wrong.

Adding enough PO4 and NO3 to be non limiting is the key, and adding some PO4 does help vs none at all.

So you are better off than some past advice, but it's still wrong.

Take atoms and weight their individual weights.

1 P and 16 N's, note, RR does not address weight.

P= 30.97 g/mol
N= 14 g/mol

30.97/14 = 2.2 x error in adding too little

Converting to weight

16/2.2=

1: 7.3 P:N.

Converting to PO4 and NO3, about 1:10.

So 2 ppm and 20 ppm is not a bad target.
I'd still rather have more PO4 than NO3, as most keep tabs on NO3, not PO4 or K etc.

As long as you dose excess P and K, etc, CO2, then NO3 is all that's really left.


Regards,
Tom Barr