Quarantine ammonia - am I missing something?

[Si4geckos]

I set up a tank about 3 weeks ago to use as quarantine. It's about 50L glass rectangle.

I put in a heater, sponge filter which has been in another tank for a year or so and a second small power filter with some media from the fx6 main tank filter. Also added a lump or two of alfagrog from the main tank.

I quarantined x2 small PLECOS and 20 shrimp.

I got ammonia every day and ended up doing 70-80% water changes once or twice a day to cut the ammonia down. Barely fed them at all.

Despite the ammonia the plecs are now in the big tank and shrimp in another established tank and all doing well. The quarantine tank has no inhabitants or food. 3 days after being left empty, ammonia has gone from 0.5ppm to over 2ppm.

What could possibly be causing the rise in ammonia with nothing in there other than 2 filters, a heater and water?

I could do with getting the tank sorted as I want to use it for fish, but it's weird results with no stock?

Ideas welcome.

[BalloonMolly]

If not in the tank, is there any chance there's something decaying in the filter media itself?

[Vale!]

I guess a list of some theoretical/possible contributors to ammonia generation in a 'bare' glass box with filtration could include :

Excess food rotting (as you mention ; though it could still take quite a while to decompose if, say, it was drawn deeply into the filter media?) ;
Nitrifying/denitrifying micromunchers dying off (mainly on filter sponges etc.) ;
Bacteria not concerned with nitrifying/ denitrifying operations dying off (mainly in water column and in the ...) ;
Biofilm (sheet of 'slime' that covers everything in-tank with a mini-ecosystem) if it's suffered some kind of misfortune ;
Macro or micro algae that's colonised the tank surfaces (and/or biofilm) dying off ;
Micro algae in the water column dying off.

I can't think of any other obvious candidates that might be present in your glass box. One or two of the above can be sent home without charge, I think, 'cause they're too fanciful in context!

I feel in my water that the answer may lie (if not simply in 'excess food rotting', of course) in more than one assembly of nitrifying microblighters dealing not only with huge and unusually-frequent water-changes (inc. dechlorinator?) but just possibly with each other, too. Maybe. How old respectively are the two tanks which donated the media : if one is relatively new and the other one has been running for much longer, the microblighters may be quite different and may not like each other much (I don't know that for sure but alleopathy really is a thing)!

Can we dismiss thoughts of temperature or pH or other weirdnesses during water-changes? Change-water was straight from the tap? I'm thinking that if it wasn't allowed to sit while dissolved gases reached equilibrium with atmosphere then, again because of the volume and frequency of water-changes, the CO2 and oxygen concentrations in the glass box must have been continuously pretty much the same as the pressurised mains water. Assuming that water-changes in the two source tanks were of a 'normal' volume of (say) 20% weekly, the nitrifying microblighters that came from there must never have experienced near-mains-water conditions before - and they can be quite picky when they want to be, by all accounts. Maybe that could have nobbled them?

Occam's Razor is screaming 'Fooood', though! Were you able to track what nitrite has been doing?

I'm boring myself! I'll shut up now.

[Except to edit to acknowledge BM's interposed post - he's got the same shaving kit as me!]

[plankton]

I have to ask this but did you empty the water in the bag into the tank? (I know it can be best with shrimp transfers)
If you did, did you test it before to see whether it was the same as in the tank?
I'm thinking well out of the box as I can only guess that whatever food you did use has been left.

Are the readings ok in the other tanks?

[Si4geckos]

If not in the tank, is there any chance there's something decaying in the filter media itself?

Maybe, but rather unlikely. The media was fairly clean when it went in the filters and barely fed the tank to get anything substantial sucked in.

[Si4geckos]

I guess a list of some theoretical/possible contributors to ammonia generation in a 'bare' glass box with filtration could include :

Excess food rotting (as you mention ; though it could still take quite a while to decompose if, say, it was drawn deeply into the filter media?) ;
Nitrifying/denitrifying micromunchers dying off (mainly on filter sponges etc.) ;
Bacteria not concerned with nitrifying/ denitrifying operations dying off (mainly in water column and in the ...) ;
Biofilm (sheet of 'slime' that covers everything in-tank with a mini-ecosystem) if it's suffered some kind of misfortune ;
Macro or micro algae that's colonised the tank surfaces (and/or biofilm) dying off ;
Micro algae in the water column dying off.

I can't think of any other obvious candidates that might be present in your glass box. One or two of the above can be sent home without charge, I think, 'cause they're too fanciful in context!

I feel in my water that the answer may lie (if not simply in 'excess food rotting', of course) in more than one assembly of nitrifying microblighters dealing not only with huge and unusually-frequent water-changes (inc. dechlorinator?) but just possibly with each other, too. Maybe. How old respectively are the two tanks which donated the media : if one is relatively new and the other one has been running for much longer, the microblighters may be quite different and may not like each other much (I don't know that for sure but alleopathy really is a thing)!

Can we dismiss thoughts of temperature or pH or other weirdnesses during water-changes? Change-water was straight from the tap? I'm thinking that if it wasn't allowed to sit while dissolved gases reached equilibrium with atmosphere then, again because of the volume and frequency of water-changes, the CO2 and oxygen concentrations in the glass box must have been continuously pretty much the same as the pressurised mains water. Assuming that water-changes in the two source tanks were of a 'normal' volume of (say) 20% weekly, the nitrifying microblighters that came from there must never have experienced near-mains-water conditions before - and they can be quite picky when they want to be, by all accounts. Maybe that could have nobbled them?

Occam's Razor is screaming 'Fooood', though! Were you able to track what nitrite has been doing?

I'm boring myself! I'll shut up now.

[Except to edit to acknowledge BM's interposed post - he's got the same shaving kit as me!]

The big tank has been going about 4 yrs and the sponge filter has been in the other tank about 18 months, which has also been going 3/4 years overall.

I've barely fed the glass box as sticking was so low and already getting readings for ammonia.

As the 2 main tanks are very well stocked I usually do 50-70% water changes per week to reduce nitrates. Straight from the tap with prime or safe added to the tank before refilling. Been fine for years. Appreciate the thoughts/ ideas.

[Si4geckos]

I didn't. I know you're meant to slowly acclimate them, but I took a risk and plop and dropped them. I spoke to the person j bought them from about their water pH, temp, etc and it was very similar to mine.

I tested the other tanks and all readings normal. 0 ammonia and nitrite, and about 30ppm nitrates a week after water change, which drops to 5/10 ppm post water change.

The shrimp are in a hang on the side breeder box OK the side of the main tank. Just came home to 3 being very berried so they must be fairly happy. The 2 plecs are in the main tank and coloured up beautifully too now. Just the empty box I'm struggling with ironically haha.

I have to ask this but did you empty the water in the bag into the tank? (I know it can be best with shrimp transfers)
If you did, did you test it before to see whether it was the same as in the tank?
I'm thinking well out of the box as I can only guess that whatever food you did use has been left.

I'll pull the little power filter apart and see if there's anything obvious in there.

Are the readings ok in the other tanks?

[plankton]

The only reasons I can think of offhand are these:
The water parameters (ph/hardness/temperature) are different, or at least have been, causing the munchers to go dormant.
You have been feeding more than you think and, as plecs are quite obliged to provide lots of waste, there is some chance of toxins. (I don't count the shrimp as being toxin makers)
There weren't as many munchers in the media as you expected.