Overstocked or re-cycling?

[fishdoc]

Hi guys. Relatively new fish keeper here (1 year). I have a 123litre (32.5 gallon) fluval mega-flex. I had this running for almost 10 months, fully cycled with no issues with water quality (Ammonia and Nitrates always 0 with 10-40 nitrates). I decided I wanted to change the tank a bit, because I was adding 2 bolivian rams and corydoras, so i switched out the gravel for sand substrate and also removed a large castle decoration for some wood as well as some plants instead (3 sword plants). Since doing this I have struggled with ammonia and nitrite reading (ammonia 0.25 but nitrite 0.25-1.0!). Nitrates remain around 20-30.

I have been able to keep the levels from doing any harm to the fish by using ongoing dosing of seachem stability but this has been going on for a number of weeks now. I am trying to decide if I have essentially re-started the cycling process with the changes or if my tank is overstocked to the point that beneficial bacteria will never be able to keep up and I need to return some fish?

In the tank I have: 5 corydoras, 2 bolivian ram, 2 honey gourami, 10 cardinal tertas, 3 guppies, 1 otocinclus and 2 hatchet fish.

I have the standard filer that comes with the fluval and instead of carbon in the second slot for the foam I have added two more packed of biomedia to try boost bacteria numbers.

Does anyone have any thoughts on this? Overstocked or can it take many weeks for the aquarium to restabilize and it is possible to get rid of all ammonia and nitrite without needed ongoing stability chemicals?

 

[Colin_T]

Do a 75% water change and gravel clean the substrate any day you have an ammonia or nitrite reading above 0ppm, or a nitrate above 20ppm.

Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

 

[xxBarneyxx]

I wouldn't say the tank was overcrowded. I think a combination of a couple of things has caused your tank to need to be cycled again.

The beneficial bacteria live in the substrate and other surfaces of the tank along with the filter. Removing the old substrate removed a bunch of beneficial bacteria. It also probably kicked a bunch of rotting organics into the water column and possibly the filter which in turn creates an ammonia spike.

Add to that the extra bio load it is is enough to tip it over to a point the BB you have left are not quite enough.

Colin's advice is a great place to start.

I would also be weary of using the seachem stability. I don't know exactly how that brand works but a lot of similar products can lock the ammonia in a form that the BB can't access, therefore the BB never grow and the issue goes on forever. May not be the case with stability but worth looking in to.

Some other steps that will help:
Make sure the filter is clean of debris. DONT wash under tap water. Use dechlorinated water or water taken from the tank and clean out the sponges/biomedia.

Add fast growing stem plants and floating plants. These will help rapidly remove the Ammonia from the water and afterwards will help keep nitrates down.

Overstocked or can it take many weeks for the aquarium to restabilize and it is possible to get rid of all ammonia and nitrite without needed ongoing stability chemicals?

Yes it can take weeks for a BB colony to grow to a size were it can cope with the new conditions. You are basically now in the middle of a "fish in" cycle. If it was me I would buy as much fast growing stem and floating plants as I could as this will greatly speed of the processing of ammonia. If you are on facebook have a look for local fish groups. You might find someone on there that is willing to give away cuttings and spare plants to help you out.

 

[fishdoc]

Thanks very much to you both. My main concern was the overstocking issue (and in that case I'd never get to the end!). If its just a case of keeping up with water changes and giving it time that's ok. Thanks again!