Overfeeding is the most likely cause. Bottom feeding pellets should be removed after 30 minutes (60 minutes tops) because they release ammonia within minutes of being added to the water. The longer the uneaten food is in the water, the more ammonia that will build up in the water and the more chance of something bad happening.
High nitrates and dirty gravel and filters can also cause infections in the brain and this can cause fish to spin out of control. Generally once a fish starts spinning, it will die.
Yep, pretty sure you're right and it was the overfeeding. It was unusual for me to drop two of those corydoras tablets in there, they're the FishScience corydoras tablets,
you can see them here, supposed to be a good quality and worked on by Ian Fuller, but they are quite large, and I normally chop them into smaller pieces and feed half- 1/3 of a tab depending on the tank. But the fish in that tank had been getting through one tab chopped into smaller pieces most times pretty quickly, only cut up so that everyone would get a chance to eat it. This time I gave two tabs, and got distracted playing around deep cleaning and arranging the other tank, and didn't monitor how fast they were eating or if any was left. Big mistake! I fed them at around 7am, and saw the cory in trouble at around 6pm, so there was plenty of time for whatever was leftover to spike the ammonia.
Some of the plants are struggling in the tank a bit, I'm sure that's not helping, found the one with rotting roots, but the ones that aren't thriving also aren't helping take up ammonia. The sand and the filter are clean though, since the tank was only set up mid- May, and I always substrate clean during weekly changes. Must be the ammonia/nitrites that killed my poor cory
Weird that it killed one relatively young cory and possible a couple of shrimp, but elderly guppies and tetra haven't shown any ill-effects, and most of the shrimp are okay as well. I guess we never know which fish may have some underlying stressor that makes them more vulnerable.
Does the filter not pull past 60% drained? If it is the input tube inlet too high, perhaps you can extend it lower. My HOB will pull to around 75%, albeit with not much flow.
Yep, I have another model of the same type of canister that I intend to steal some of the intake tubing from to extend the length of this one, but my cories gave me a big spawn that are now growing out in a different tank using that canister, so that plan got delayed! lol. I do have other filters though that I plan to do some juggling around so I can extend that filter intake. This tank has the canister filter plus a smaller internal nicrew filter in there for an extra boost and for flow.
That is a high nitrate level, and in my opinion cory's hate nitrates.
I agree. It's unusually high for this tank, for any of my tanks, which is why I wondered what was pushing it so much higher than normal, since there must have been something producing more waste than usual, that not being used up by plants but processed by BB, and meaning I had higher nitrates than is normal. Usually nitrates are between 10-20ppm before each weekly water change, which is about where I'm comfortable with them being. Lower always better, of course, but as long as it's not going above 20ppm I don't worry. The ammonia/nitrites/nitrates were all unusual.
Chill out dude, she’s already said it’s unusually high so will be taking steps to fix it and get back to the normal range things like this happen there is no point jumping on people’s backs when you can see they are trying to fix them.
Thank you.
He was right though, that they are high and cories are sensitive to that (so are shrimp and lots of other fish, to be honest) although I think
@itiwhetu and I agreed to disagree long ago when it comes to cory keeping, substrate, barbels etc! But he wasn't harsh
Update: I did large daily water changes and tests on the tank since I posted, haven't lost any more fish *touch wood*, and I've fasted the fish while I continue trying to fix the tank. They had a light feed of bug bites today, ten minutes prior to a water change so I could clean up any uneaten food.
Still figuring out what to do long term... I suspect it's partly that it's still a pretty new tank, and that it's pretty heavily stocked with 15 cories, two (granted, still pretty small) plecs, plus the odds and ends of the tetra and guppies. I got used to having this lot in a long established 57g, and that they're now in a 34g, which is still struggling to get established in terms of plant load. I need to get some more fast growing plants in there I think, and I'll likely switch to twice weekly changes, at least for now, and be much more careful about how much I'm feeding of what.
