They spawned for the first time about three and a half weeks ago, completely unexpected and a bit complicated as other fish in the tank decided to spawn at the same time, as well as some in another tank. The Corydoras spawn missed out on much of my attention, I rescued two eggs from the sand and put those in a holding tank and as a result have two fry. The others were lost. I thought they would be OK in the tank, there's nothing in there that would eat them and so I half-expected, half-hoped that I would be able to catch some of the fry once the eggs hatched, most of them seemed viable and there was, I estimated, a couple of hundred. However, no fry
No idea what happened. In the mean time, I had farlowella, sturisoma and L010a fry to try and get eating (I can get them to breed but limited success rearing the fry so far) so those had my attention and the two corydoras were in with them and have been doing very well.So this morning I was really excited to find they had spawned again but what bad timing yet again! I'd been having issues with the filter in that tank since I broke a catch on the impeller plate which didn't seem that important at the time but has caused problems. Work is busy so I was hoping it would limp by for the week. It's not a densely populated tank though and has a good air current as well as another pump I've been testing out so I wasn't too worried. I had bog wood a few plants and some java fern in there but it wasn't well thought out and I decided I needed to start again with it. I removed all of it (still hoping to find some corydoras fry but nothing).
Got up two days ago and the water was a bit cloudy. The fish seemed fine though so I thought it was probably bacterial bloom and got on with other stuff. Got up this morning and it was worse. The fish while not showing real distress didn't seem too happy and it was while I was testing the water to see what was going on that I noticed the new eggs. The tests showed very high nitrates (but fortunately ammonia and nitrites were fine) which I can only think were due to disturbing the substrate so much, although I had done a big water change at the same time. Also the pH which is usually around 7.4 was down to 6.9. Fine, so I would do another big water change but of course there's eggs all over the place. In the end, I decided to try and remove the eggs which were highest in the tank, allowing me to take a few inches of water out and replace, then syphon again, replace etc until I had changed enough water for the fish to be happy.
While I was doing that, my OH took on the task of trying to sort out the filter, the output of which had slowed to a trickle. Turns out the impeller shaft had snapped and the filter was quite blocked with debris from all the messing about in the tank AND 10 little corydoras fry who were living in there perfectly fine from the spawn three and a half weeks ago! Not only had they survived the filter and the high nitrates, I had also noticed, while rescuing eggs from this spawn, that the water was a bit cold - turns out the heater had got switched off some how. I am usually so careful about such things but I think it must have been off for a couple of days, no wonder the fish were not looking happy, it's usually 79F but was down to 69F. I'm amazed they spawned in such poor conditions and even more so that those fry survived - still don't know what happened to most of them but I hope I get a few more fry this time around. The filter has been repaired with a cannibalised one and the intake is firmly covered with foam. Water quality is back up to a reasonable standard and I'll carry on monitoring it and doing water changes until it is perfect. I have maybe 60 eggs in a container with air and the rest remain in the tank, I'll see what happens this time but try my best to pay more attention!