, I am confused when it comes to GH numbers. Currently iam on 20Ca and 5PPM Mg using 100% RO . What factors (high micros, high macro, light ,co2 ?)decides if i need to 40:20, 20:10 or 20:5 (Ca:Mg) . Any pointers on this please? Your numbers looks close to EI i guess.
Macros are roughly EI but like Greggz said, with 75% water changes instead of 50 the levels in the water column arent as high as they would be doing only 50%
You can play with the nutrient accumulation calculator here to see the difference. https://rotalabutterfly.com/accumulation-calculator.php
Assuming zero plant uptake, which you have to do with this, the difference in NO3 levels dosing my 7 ppm 3x
Doing 50% weekly water changes the total NO3 in the water column eventually levels out around 42 ppm.
Doing 75% the maximum level becomes around 27 ppm. Again this assumes zero plant uptake just for the sake of comparison
So...water change volume plays a big role in how much nutrients are actually in the water relative to the dosing amount
I do bigger water changes for dissolved organics, for cleanliness, not to reset nutrients.
My tap has around 40 ppm Ca so Im locked into dosing Mg/K around that. Personally I think the hobby in general under doses Mg. My tanks have always done better with higher Mg levels, a 2:1 Ca:Mg ratio works best in my set ups.
20 Ca should be fine, Id run 10 Mg a long with that but its something you'll just have to try and see if it works better