30G + ammonia question

[PicklesandBeans]

Getting back in the hobby. It’s been a saga. Will try to be clear without being long winded.

Have a 30 G tank we were using the fatten up our baby koi before releasing them into our outdoor pond. All 6 were about 2-3” max. Had two filters (canister and HOB) - both alone should have been more than sufficient but koi are poopers so we had both going. Had A little gravel and 5-6 different plants. We could never get the TAN lower than 1 ppm and had to do daily 10G changes, and maybe a 20G change every other week. We hadn’t cycled the tank first (it was initially an emergency makeshift ICU for another koi- that’s another story) and figured we were being aggressive with the feeding so we put up with this for 2 months. Used the Prime/Seachem? Tank stabilizer plus those clear balls of beneficial bacteria.

We released the koi. I kept about 10G of the same water in the tank and then tried my hand at my first aquascape. Took off the HOB and only had the canister. I rinsed off one of the canister filters in the aquarium water to “clean” it without removing all the bacteria. Didn’t even touch the bioballs/other layers. At some point, we checked our tap water to confirm no ammonia/nitrites/nitrates. Had the tank up and running for a week without fish. We had some miscommunication (I thought he checked the tank, he thought I checked the tank) and basically thought the tank was ready to go for the fish. So then we put ten Exclamation Point rasboras and two small guppies (full size <1”) and two cherry shrimp into the tank. Then realized we hadn’t checked the water which then showed a TAN of 2 ppm at 6.6-7.0 pH. Did a 10G water change (we use prime for our tap water). No one has died yet. Lol.

Checked that one chart w pH, temp, TAN to figure out how much ammonia was actually in the tank and it seems negligible which is great. There are no rotting plants. We feed like a pinch of ground up food once a day. So my questions:

Do I just need to suck it up and replace all the water to get the TAN down as low as possible?

Will the bacteria (wherever they are) eventually get rid of the ammonia/ammonium? Am I actually worrying about nothing?

The fish are so small - can they really cause that much ammonia?

Why didn’t my tank cycle after all my poopy koi?

Thanks for reading this saga and for any advice!

 

[ColdKoi]

There’s many factors involved but running the tank with no fish or ammonia source would start to starve and kill the beneficial bacteria within a couple days.

To say you’re starting from scratch is probably a long shot but you’re going to be set back a little. But it seems it doesn’t take a lot of established bacteria to quickly repopulate. Just keep up on the water changes to keep it manageable for the fish, you don’t want to get carried away and try and get everything 0 or you’ll just be prolonging the process

 

[PicklesandBeans]

Thanks ColdKoi.

In terms of water changes, it seems that (according to that pH, temp, ammonia/ammonium chart) the TAN can get pretty high before the ammonia becomes toxic - at least with my current tank parameters (I think it was upwards of 8 ppm).

Do you have thoughts about keeping it under a specific threshold (or at least attempting to)?

Someone also mentioned to me that it could be the new substrate in the tank. Have you heard of that happening? It was one of the common brand ones, specifically for shrimp and planted tanks… small round brown balls of soil (sorry - forgot the brand)

 

[Aiken Drum]

Your target should be to keep ammonia + nitrite combined below 0.5ppm through water changes. You are right about TAN and it actually being the free ammonia being the actual toxic part of the equation but i would still try to keep below that 0.5ppm combined target. Its your safety net. pH could shift as your tank settles down and what was non toxic could quickly become toxic for instance.

Bacteria will survive without ammonia for a few days if kept wet, a few weeks if kept wet and oxygenated. If you kept the filters running it shouldn't have died off to any degree without fish, but if you turned off the filters then it could have died off.

Yes. That type of substrate can definitely contribute to ammonia for a while.