My Google-fu is weak, and I can't any specific details regarding adjusting fertilization plans to account for fish food and waste. Is this a significant factor?














Does anyone have any links or other info to share?


Thanks!


(also, is it just me, or are there no breaks between paragraphs?)

Hello, in a tank with plants and fish, if deficiencies show up it would tend to be iron, calcium and potassium.

I have low tech tanks only, with soft water from the tap, so I add a remineralizer anyway (adds Ca for sure) and waited for signs of other deficiencies before starting any other fertilization routine.

There are others far more knowledgeable on the specifics who will hopefully chime in, but the main contribution of fish waste relevant to plants is probably nitrates. Many folks with a higher stocking of fish will reduce or eliminate dosing of KNO3 (potassium nitrate) for that reason, and will substitute K2SO4 (potassium sulfate?) to ensure there's enough potassium. This is particularly so if the fish at issue are sensitive to higher levels of nitrates (I've read that cardinal tetras are one such fish, although I can't verify that).

Bump: Just you. Huge gaps between your paragraphs showing for me :-)

Thanks both of you.

I'll try lowering the KNO3 and raising K2SO4. I had actually noticed what looks like a K deficiency (pinholes). When I raised the overall dosing levels to address the problem (while sticking to the standard EI ratios) I got algae right away...maybe the nitrate going too high because it was essentially already being dosed via fish food.

The breakdown of the fish waste eventually ends up nitrates. The NO3 in the KNO3
is contributing more to those nitrates. The K2SO4 has no NO3.
Suggested level of nitrates for a planted tank is different depending on who you ask, but
between 5 and 30 is both of the extreme levels that I have heard. So I try for 10-20.
Those two are even enough in "K" value to swap them evenly. Best time to test is just before the water change. Using a 50% per week water change as an example, you will get a better reading on or after the third water change. At that point I would trust that the reading would not change significantly after that. I'd still test just before each water change to make sure you didn't remove all of the nitrates. But if you are using all
KNO3/w no K2SO4 then doing a 50% split would be fairly close if you were getting a red test result before. Hope that is useful to you.

Before you add any fertilizer check the NO3. This will be all from fish food. See if it builds up or drops through the week between water changes.

If the level is zero or close to it, then the plants are using pretty much all the fish food. You could follow the estimative index or any other fertilizer program, without any adjustment.

If the level is low, or fluctuating, then the fish food is supplying a certain amount of nutrients, so you probably want to follow a modified program.

If the level is high enough to need water changes to keep it low (under 20ppm is a good target) then the fertilizer program would be greatly altered.
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Fish food supplies reasonable amounts of:
N, P, most traces.
Fish food is low in:
K, Ca, Mg, Fe.

Water changes, with GH at least 3 German degrees of hardness supplies Ca and Mg. If the GH is less than that, or you suspect the GH in the water is just from Ca or just from Mg, you might want to supplement it with whichever is missing. This is not dependent on fish food. It depends on the tap water.

If the plants are using pretty much all the N, then they are also using all the other elements. Fertilize with all the macros and micros at 100% of whatever program you are following.

If the plants are using most but not all the NO3, and you need to supplement. Lets say you find that 50% of the dose suggested by your fertilizer program is needed to keep the NO3 in the range you want.
Then you should also dose:
50% of the suggested P, and traces.
100% of the suggested K, Fe.

If the plants are not using much of the NO3, and you are doing water changes to keep it low, then there is also an excess of P, and plenty of most traces.
Supplement with K, Fe.

Happens to me too when trying to post a new thread since the facelift/update. You can see the skipped lines after posting, but while creating the thread it doesn't show that you actually are skipping lines (I used to press "enter" then a letter then "enter" again to see the skipped lines) so you press "enter" a lot trying to get it to work (hence the huge gaps). Not sure if the mods are aware of this issue or not (I think I recall this happening when typing in "advanced" replies as well), but sounds like it only happens to certain users (for whatever software reasons).