Sudden Nitrite Spike (Established Tank)

[Bryan Dismas]

Hey guys,

Just wanted to see if this happened to any of you, and what you did to resolve it.

I've had my 20 gallon tank for ~5 years and I occasionally test for ammonia/nitrite (last time was about a month ago) with consistent readings of 0. Just today, I came home to find 3 fishes (1 Cardinal Tetra, 2 Buenos Aires Tetras) and 2 of my yamato shrimps dead. The rest of my surviving fishes (an Angel, a Cardinal, a Buenos Aires, 2 Otos and a L183) were visibly gasping at the water's surface (looks like I got home just in time to save them).

Either way, I instinctively performed a 60% water change and dumped a ton of prime into the water (about 2.5 caps). In an hour the fishes appeared to be back to normal (The angel had lost almost all its color, but it returned after the large wc/prime treatment). My initial suspicion was CO2 poisoning (since adding pressurized CO2 was something I had done recently after deciding to try converting to a planted tank), so I stopped the CO2 and turned on my air pump (running a sponge filter off it). However, after which I measured all my parameters to find 0ppm ammonia but 0.2 - 0.5ppm nitrites and about 10ppm nitrates. So ultimately, I think it was nitrites that caused the fish to gasp and not the CO2 (drop checker seems to confirm this, as it did not appear light green).

Anyway, I'm trying to identify the cause of the problem so here are a couple of things that I changed lately (in chronological order):

1. Increased heater temp from 28 degrees to 30 degrees (was treating what appeared to be Ich on an Oto with heat) -> 2 days ago
2. Increased algae wafer feeding regimen (from 1 wafer every 2 days to 1 wafer a day) -> ~3 days ago (this may be the reason for the spike, though I could not find any uneaten bits of it)
3. Added a significant plant mass (would consider it to be light to medium density) -> A month ago
4. Running CO2 at 1bps and following the "beginner" dosing for seachem line of liquid ferts (macros twice a week, micros twice a week) -> 2 weeks ago

Also, until my biological cycle properly reestablishes, this is what I'm going to do every day:
1. 50% water change in the morning + prime double dosage
2. Test params then 50% water change in the evening + prime double dosage -> once nitrites hit 0, I'll do 50% wc on alternate days until I get a reading of 0ppm nitrites 3 times in a row.
3. Stopping CO2 (at least for tomorrow, then resuming at 0.5bps)
4. Lowering temperature (back to old settings)
5. Reduce feeding (algae wafers down to 1 every 3 days for now)
6. Keeping my sponge filter running 24hours (previously it was on a timer so it only ran 8 hours a day on lights out)

I'm treating this like my tank is going through a mini-cycle, but seeing how I've never really experienced this before (except maybe once or twice after my tank had initially cycled almost 5 years ago), I'm not sure if what I'm thinking of doing makes sense (Esp the stuff related to CO2, I'm very new to planted tanks). Any feedback/comments/suggestions are greatly appreciated!

[Bryan Dismas]

Quick update:

This morning the nitrite levels seem to have dropped (from 0.2 - 0.5ppm to 0.0 - 0.1ppm), which suggests the cycle hasn't been completely halted (I suspect its not so easy to completely crash the nitrogen cycle in an established tank).

Based on this, I performed a 30% water change (instead of 50%). Will test with new test kits I just bought to get a more accurate reading tonight.

Any experts on planted tanks who think its a good idea to turn the CO2 back on? I already have it on a solenoid/timer so it only runs while the tank lights are on. One thing I did notice was that the plants recently stopped pearling almost completely (which suggests a nutrient deficiency probably due to my light dosing regime). Perhaps the CO2 started to build up and with the lowered O2 in the tank the nitrifying bacteria became less efficient?

[Urban Aquaria]

The nitrite spike does indicate the tank going through another cycle process. Most likely its all the changes you did to the tank which combined to unbalance the existing system. While adding plants can help utilize nutrients, it can sometimes also increase the amount of rotting organic material in the tank and add to the overall bio-load, especially during the initial period when parts of them melt during transition.

At this point in time, to reduce stress on the livestock, it'll be better to hold of the Co2 injection until the tank parameters are stable again. Also return the temperature back to normal (warm heated water holds less oxygen). It'll be better not to pile on more variables that may affect the fishes.

Just to check, for the Co2 drop checker... did you mix the indicator reagent with tank water? or you used 4dkh reference solution or pre-mixed indicator solution? Reason why i ask is if you used tank water to mix and your tank is using active soil substrates, then the color readings will be wrong (due to the pH and KH of the water already being buffered by the soil) and that could mean that the Co2 might actually have been too high, which may explain the fishes gasping at the water surface.

[Bryan Dismas]

Hi UA,

Thanks for the reply!

Just to check, for the Co2 drop checker... did you mix the indicator reagent with tank water? or you used 4dkh reference solution or pre-mixed indicator solution?

I used a 4dkh reference solution mixed with gush indicator fluid at a 4:1 ratio as recommended by the indicator fluid (I find its a little too dark at this concentration though, makes it really hard to see light green). I also made sure to test the 4dkh solution with my kh test kit, which did, as expected, change color at the 4th drop.

Reason why i ask is if you used tank water to mix and your tank is using active soil substrates, then the color readings will be wrong (due to the pH and KH of the water already being buffered by the soil) and that could mean that the Co2 might actually have been too high, which may explain the fishes gasping at the water surface.

I'm actually using a normal inert gravel substrate (my old substrate from before I started planting). It's supplemented with flourish root tabs though. Last time I checked, my kh was at about 3dkh with gh being at about 10 degrees. The PH is consistently between 6.2 (with CO2) and 6.6 (after lights out and stopping CO2).

Since I don't have a rich nutrient base, I had opted for EI dosing with less root heavy plants (I have Rotala Rotundifolia, Ludwigia Repens, Pygmy Chain Sword, Dwarf Cardinal Plants, Corkscrew Vals, Java ferns and Anubias). I've recently also added Pogostemon Helferi, 2 Crypts (Wendtii/Undulata), and Alternanthera Reineckii Rosaefolia/Cardinalis.

Yeap, I'm not sure if it was excess CO2 or a nitrite spike, but you are right that many of the plants are shedding their emersed leaves and growing new submersed ones, which definitely increased the bio-load by a significant amount. Last night might have just been the tipping point for my filtration system. I try to remove as much as the debris/melted parts as possible, but some of it gets sucked up by the filters before I have a chance to remove it from the tank.

Anyway, I'll take your advice to heart and try to revert as much stuff as possible to the way it was before (lowering temperature, halting CO2 and constantly aerating the tank). Since during this time the water column is probably going to be low on resources for the plants (low nutrients for constant WC and low CO2 from aeration + no injection), should I also lower the photoperiod for the plants? I currently have my lights (CurrentUSA Satellite+ fixture) on for 8 hours a day, I could probably instead lower the light intensity (my fixture is adjustable) so my tank operates more like a low-tech planted tank for the time being?

[Bryan Dismas]

Came back today, and everything appeared to be fine in the tank.

Ammonia and nitrites both read 0ppm (cross checked with my old kits to make sure).

At this point, I'm fairly certain that it may have been caused by a build up of CO2, which slowed down/paused the nitrifying bateria in the tank. I did notice that while injecting CO2 my drop checker remained green (never really returned to blue), but after stopping the CO2 for the last day with constant aeration and tons of water changes it is starting to slowly return to blue.

I'm gonna keep it turned off for now to see if the drop checker continues turning more blue, after which I will reevaluate how much CO2 to inject (and probably use less drops of indicator fluid so the drop checker isn't so dark). Gonna keep dosing prime just in case any spikes occur again, but will hold off on water changes if Ammonia/Nitrites don't show up.

I've actually overfiltered my tank (I'm running 2 canisters and a sponge) and with no sudden increase in biomass (apart from plants melting over time) the filters should not have reached their max capacity. Hence my conclusion that low O2 levels from overdosing CO2 probably was the root cause of all the problems to begin with.