Disappearing fish?

[oldbirdy]

My teenaged son has an established tank, it is globe shaped with 9 small tetra (5 bloodfin and 4 headlamp tetra, I'm not sure that's the proper name!). He feeds them daily and we do a small water change fortnightly and a large 4 to 6 weekly.

Today was large water change and we take out all ornaments etc to wash, leaving only the substrate. It is very hard to count the fish as they are semi transparent and the globe shape reflects them, but we could only see 7. 2 of the headlamp ones appear to be missing. The obvious solution is that they have died but no floating fish have been found at any point, nor were any bodies revealed during us agitating the substrate to get the waste up in the waste water pipe. We do have two nerite snails who have bred so about 20 small snails. Could they completely clear up two tiny dead fish? The fish are about 2 - 3 cm long. Or is it more likely that we are miss counting?

Yes the snails (and the other fish) would happily eat dead fish. Do you test your water weekly? They might also have jumped out if the tank is uncovered - have you checked round the back of the cabinet etc?

Just a note, both types of tetras need more of the same to feel comfortable.

You wash the ornaments?

What do you wash them with?

Just with water. We try to scrub off snail eggs and algae.

The tank is covered. I always thought we'd see dead fish, floating. I think the water was not best quality as I noted some hair- like algae on the pondweed. We have drastically reduced the amount of pondweed today too. I haven't tested the water in a while; it was perfect last time and they've been happy in there for over a year with no lost fish. I can test it again. But amazed that no trace would exist of the fish if they died.

Should I get another couple of headlamp ones? I was worried about overcrowding. It's a 30l tank.

Yep fish will eat other dead fish and pretty rapidly. Esp tetras TBH as they're tiny.

dont get any more as tank quite small

I got two more of the headlamp guys. None of the tetra grow beyond 3cm and they are smaller than that now. I have 9 fish in total so even if they all grow to max size the tank will not be beyond capacity. They had been happy for over a year before the two fish died; no other losses. The two remaining tetra of that species are happier now and they are swimming in a little gang of 4 again.

A bit late from your first post, but I don't suppose there's any chance they got caught inside the filter? I've known that happen before with tiny fish - I think they usually die quickly, though a friend found one of hers in there, still alive, after it had been missing a short time. Possibly worth checking, in case there are remains in there which may contaminate your surviving fish.

Glad that your remaining tetras are happier now

I don't think so, as I had the filter out to clean when we did the big water change; didn't find any organic matter! I suspect ds got lazy and let the water quality degrade too far; I think losing 2 of his fish as a consequence had taught him a lesson on responsibility. I hope do anyway!