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Not able to establish Full cycle - Nitrates problem

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  • Not able to establish Full cycle - Nitrates problem

    I have a very heavy stocked mbunas cichlid 80gal tank and I’m trying to create a full cycle filtering (eliminating the nitrates). Actually I’m doing 50% water change 2 times per week to keep the nitrates around 20 (reaching between 40-80 just before the water change). Then for sure my bacterial cycle is not eliminating nitrates (or not enough). I now the recommendation is not much than 20-30% water changes at times but I’m really not alone doing 50% with cichlid tank and I can’t do small water changes each day or 2 days.

    I’ve 6L of Matrix and 4L of Denitrate in an overhead filter and a canister filter. Feeding once per day. With my reading I’ll modify my system to optimize it by putting all the denitrate in the canister and lower the flow around 30GPH-120L/h and put all the matrix in the overhead filter as it’s a more oxygenated area.

    My main inquiry is about the danger if there is, for the biological filtration while doing my water changes. I’m using a Python hose water change system, siphoning 50% of the water and filling new water at right temperature directly into the tank. Before filling the tank back I put 1.5 teaspoon (7.5ml) of Safe in the remaining 50% of water. (I put more than recommended dosage as I want to help fast result of chlorine neutralization). While I fill back I start back both my filters and circulating pumps. I do that way since years and never noticed any disrupt in my biological filtration (always 0 ammonia & 0 nitrites). It’s recent (some month) where I stocked that much my tank and now try to make work a full cycle filtration to hopefully return to only one water change per week.

    I’m asking me how much times the chlorine neutralization takes by the Safe in the tank water? Is the anoxic bacteria are more sensitive and being disrupted by some chlorine circulating before it’s neutralized? Or it’s not the problem and it’s just because my system is not optimized correctly for now?

    My denitrate is for 1L mixed with my substrate gravel and the other 3L in 2 baskets in my overhead filter where I blocked almost all holes of my spray bar. As I’m digging further on the net I understand it’s not optimum at all as even wt blocked holes in my spray bar of overhead filter there’s not enough time for the oxygen to been burned in these low deep baskets and for sure it’s not an anoxic zone suitable for this process. It’ll be way better lowering the flow of my canister filter having all the denitrate on stacked baskets.

    But I’m still perplex as even without the denitrate, having 6L of Matrix at high flow rate is not nothing...

    A year ago I got it for a month having 0 nitrates. I tried a water change per day since had 5ppm nitrates and kept it there 2 weeks and Euraka! Nitrates went to 0 and stay there 4 weeks. At that time many of my fish were small and not adults. But now I can’t reproduce that result.

    Note: 0 nitrates in my tap water, use 20ml of Stability each water changes and cleaning my mechanical filtration each week.

    Another question: Some would speculate on the net that Seachem Prime or Safe binding ammonia, nitrites & nitrates (detoxify) can perhaps like starving the bacteria and perhaps prevent a full cycle to establish... Is this can be true?

    If I don't start back my filter pumps right after the full refill and just move the water with my recirculating pump to leave time for chlorine neutralisation.... How much time the biofilter can hold without water circulation?

    Thanks for your help
    Last edited by Milea; 03-16-2021, 09:11.

  • #2
    Thanks for the post, Milea!

    When doing water changes straight from a python into the tank, we recommend using the full amount of Safe or Prime for your aquarium volume before filling. Once you have added the Safe or Prime, you will then start filling the tank. This should take care of any incoming chlorine or chloramine in the tap water. Once the tank has filled, you can add a bit extra Safe or Prime for peace of mind, but it's not necessary. Safe and Prime work immediately to remove chlorine and chloramine, while also detoxifying ammonia, nitrite and nitrate for up to 48 hours. Safe or Prime do NOT lock up the ammonia, nitrite or nitrate to where the bacteria can't consume/utilize it. They are still fully available for the bacteria, just in a safer form to not harm your fish. As long as the biological media is wet and still submerged, the bacteria will not die off for a while, so you could leave your circulating pump on for a while after the fill without the main filtration, but I don't think it's necessary.

    I hope this helps!