Volume of water used for computing fertilizer dosage

[marlons]

Hello Seachem,

When computing for the dosage of fertilizer we need to add into our aquarium, do we simply use the volume of tank, or should the volume occupied by the hardscape + substrate and/or the volume of water that goes to the canister filter/sump be subtracted and added respectively?

I have a pretty deep substrate which in my estimate is between 10 and 20% of the total tank volume.

[Tech Support PE]

Hello marlons,

You can do it either way. If you want to estimate the actual tank volume for dosing, go right ahead. If you go this route I'd test to see what the actual concentration is after dosing. I normally just use the nominal tank volume and adjust dosing down a couple ppm for lightly (50% or less plant coverage) planted tanks and go with the full dose to reach my desired concentration for heavily planted tanks and/or high-light, high-growth, systems. Planted tanks are a bit of a guessing game as well since nutrient demand differs significantly based on the types of plants kept and their growth rate. My best recommendation would be to start a couple ppm shy of your target, observe your plants for a week or so, then adjust as needed to meet apparent demand.

Kind regards,
PE