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Discussion Starter · #1 ·
I have a 45 Gallon planted aquarium that has been established for nearly 3 years. Carbon injection, UV sterilizer, etc. Up until now everything has been going very nicely. Great plant growth, happy fish, etc. Normally I do water changes 25-30% once or twice a week. I waited WAY too long between filter changes this time though, and now my tank is stuck in a repeating Nitrite spike that goes like this: Wake up and the fish are all on top --I do a partial water change. Lights come on at 10, fish are once again on top --I do a partial water change. Everything is normal throughout the day, but the process repeats itself over night, always the same.

If I didn't have fish in there, I would just let the tank cycle normally without the water changes, but I have no where to put the fish and I really want to save them as much as I can. But I can't keep doing 2-3 water changes a day. I'm getting nowhere. Here is the water chemistry:

PH: 6.5-7.0 depending on Carbon doser
Ammonia- 0-.2ppm
Nitrite- Between 1.0-2.0ppm
Nitrate- 0-5.0 ppm
KH is around 125ppm last time I checked, but the water is buffered and the plants are fine

I have heard about adding ammonia, etc. to ease the nitrogen cycling but I don't know anything about any of this. I would appreciate any advice to keep the fish alive and get through this cycle.
 

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Do you know anyone with a tank in your area who can potentially give you some already-cycled filter media to help boost the bacteria in your filter? That would cut the recolonization time down considerably and reduce the number of PWCs you'd need to do.

You might also try getting some commercial bacterial cultures (though people have varying opinions on the efficacy of bottled bacterial cultures, it would be worth trying). There are several brands sold at most shops that should work.
 

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For emergency ammonia relief I would use purigen. The purigen will slowly get loaded down with ammonia and nitrates making it less effective while the bacterial colonies are growing and spreading. Once the tank has stopped cycling remove the purigen, soak it in bleach to recharge it then put it aside in case you need it in the future.

I would also cut the CO2 until everything is balanced. I would also throw in a bubble wand to make sure the fish are getting plenty of oxygen.

Unless you took the entire tank apart and scrubbed it there is still a considerable amount of nitrifying bacteria left on all surfaces of the tank, just not enough to handle the current load. I doubt introducing bacteria from another tank or a bottle will help.
 

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Discussion Starter · #5 ·
Update: Thanks for all of your help. I appreciate it. So after listening and reading a lot I decided that I needed to get a bigger of what was going on. I did a 50% water change and did not feed the fish for two days. Then I did a bunch of tests. To my huge surprise the Nitrites test came back as zero, along with the ammonia test. So it wasn't adding up. I tested again. Same thing. So why are all my fish swimming at the top, circling, every morning and every night? There were elevated Nitrites at first, but it was never to the extent that the fish symptoms were matching. AND --something I forgot to mention, my 3 Spot Gourami didn't seem to care at all. Then it dawned on me ---OXYGEN STARVATION. Prior to all the problems I had cut back my 2 largest plants. These guys grow like crazy so I cut them a lot. I have very little circulation in my tank mainly because of the large plants. When I cut them they must have temporally slowed down their growth rate or something, and now the water was low on oxygen. That explained why the fish were fine during the day, yet swimming on top at night. It also explained why there was more CO2 in the tank than normal (plants were not using it up). I immediately put in an air stone and a few hours later every fish is back to normal. The plants started waking up today, and my carbon injection kicked on for the first time in a week. I ordered a small power head and I am going to introduce some aeration and current into the tank so this does not happen again. I think I have a lot of PTSD from past nitrite spikes killing entire tanks off. I just assume any wierd behavior is always nitrite-related.
 

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When the lights go out plants will take in oxygen from the water and put out CO2 compounding your O2 problems.

I am happy to hear that you got everything under control!

I never worry about oxygen in the water because I use sumps in a trickle filter configuration which provides plenty of O2 exchange. But I always worry about lack of O2 when using a sealed system filter like a canister filter. A spray bar on the canister return is another way to keep the oxygen levels in the tank up. I recommend putting the spray bar above the water level which exposes the returning air to plenty of oxygen as well as agitating the surface water in the tank which can be insulated from O2 by biofilm etc. when the surface isn't agitated.
 
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