Safe to 'add' nitrates to a tank using wastewater from other fish tanks? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 01-04-2016, 05:58 PM Thread Starter
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Safe to 'add' nitrates to a tank using wastewater from other fish tanks?

I'm sure like many of you, you have more than one fish tank.

Some of my tanks are stocked with fish and plants, some are just plants.

Aside from nitrates though, I'm not positive which 'bad' items are being removed from the water column in a water change, and with something like nitrates it's more a matter of the concentration than strictly being bad or good.

So if you have a tank that's basically all plants and no fish, would there be any harm in 'cutting' some of the waste water that's high in nitrates with the typical tap water when doing a water change?

Is it silly to even consider this option?

Should I just find a fert. to add nitrates (and nitrates only) instead, and remove the variables that would come into play by using other tank water?
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post #2 of 3 (permalink) Old 01-04-2016, 09:55 PM
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I've done something similar in the past... I will top of my 3g tank with water from my 25 (shrimp in 3 fish in the 25) only issue I've noticed is I tend to build up much more surface film doing it this way that with tap water, which leads me to believe with no way of testing it, that in also adding a large amount of dissolved organise to the tank as well
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post #3 of 3 (permalink) Old 01-04-2016, 10:45 PM
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I do not think that is a problem at all! Very good way to get nutrients to the plant-only tanks, and 'treated' water to the aquariums with fish. It is almost like adding a planted refugium to the tank, and getting the advantages of a larger water volume to dilute the wastes, and the removal abilities of the plants.

A few cautions, though:
Do not add medicated water to the plant tanks.
a) whatever you are medicating the fish for can get into the plant tank, and might then spread to your other tanks as you share water changes.
b) the medication has a certain dose and timing to properly kill the disease or parasite. To remove the water with its load of pathogens to a non-treated tank halfway through a treatment is to risk encouraging antibiotic resistant diseases.

Test the water parameters (GH, KH, TDS, pH) when you are adding water back to the tanks with livestock. Fish prefer these parameters to be stable, with not a sudden big change. If the GH, KH and TDS drop by 10% or rise by 15% these are safe for even the more delicate fish. A greater change than this may not be safe.

Fish food is high in N, P, and most micros.
Fish food is low in K, Fe, Ca and Mg.

If the water in the fish tank has high NO3 from fish food, then your planted tanks may still need you to add potassium and iron. Monitor the GH and make sure it is not lower than about 3 German degrees of hardness, or you can dose a GH booster like Seachem Equilibrium (contains potassium, too) just to be sure the plants will get enough Ca and Mg.
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