24ppm NO3 and 3.9ppm PO4 / week?

hi. my suggestion for the best rate between NO3 and PO4 is 10:1, which represents the Redfield Ratio. this doesn't mean that you should try to reach to these values (10ppm NO3 and 1ppm PO4). depending on the mass of plants from your tank, also 20ppm NO3 and 2 ppm PO4 would be better for a larger number of plants.

 

EI means dosing enough to prevent dificiencies, but some of these values are quite high. Not that it would cause a problem, but I don't really see the point of loading the watercolumn if there's no need to. 3x per week 3 ppm of KH2PO4 is overkill IME. I have a heavily planted tank, but it consumes no more than 2 ppm KH2PO4 per week.

Of course consumption is also dependent of light. More light = more growth = more consumption of nutrients. Even so I have a hard time to believe that 9 ppm of KH2PO4 would be consumed on a weekly basis.

EC would suffer a lot also.

Ratios are of non importance. I couldn't even tell you the current ratio N in my tank. It's all over the place. I can see no difference in plant development or growth, or in the ratio aspect to algae.

Since GH is a addition of Ca and Mg ions, one can't tell how much of each is present. A GH of 10 can be all Ca and almost no Mg. I've varied Mg between 2 and 15 ppm without noticing differences in plant growth. But because we can't determine how much Mg is actually present, it's better to dose it. IME 5 ppm is a good average.

 

About the need to add magnesium. Try the website of your water supply. For example, I live in Utrecht and the entire water quality test report is found online on vitens.nl. Ca 40ppm, Mg 4.6ppm so I add a little magnesium every wek after water changes. But with only knowing GH, you know nothing, you need to know at least Mg or Ca as well.

 

tapwater in NL has enough Mg in general, but if you just use RO you have to add both. Positive Ca ions also relate to fish health (osmotic pressure)

You could do a 50-50 tap/RO mix and save yourself the trouble of makong a lot of RO, getting rid of the things you then need to add again....

 

I gradually moved my PO4 close to that. I was getting terrible green spot algae, so over the course of 3 weeks I added a little more each dose. I'm now close to 3ppm 3 times a week. GSA is gone and plants are doing great.