Can you share some pics of the tank(s) please? They are bottom dwellers, and will have favourite hidey spots, and lazing around times. But if they're always inactive and hiding away in one area, it does suggest there is something wrong.
Seeing the tank will help. The decor/set up/planting/hardscape etc do affect how safe and secure they feel in the tank, and that will affect their behaviour, and there are lots of small changes you can make that will help them feel more secure, but really need to see the tank to be able to make suggestions.
Also which species of cory are they? Albinos are a colour mutation of a species. If you have pics of the cories, we can ID which ones you have. Albino
Corydoras aeneus (Bronze cories) tend to be more active and confident, but you can also have albino
Corydoras Sterbai, or albino
Corydoras paleatus.
Sterbai tend to be naturally more shy, and mine also tend to isolate themselves and be less active unless it's feeding time, but there are still things you can do to help.
paleatus are also available in an albino colour mutation, and they like a cooler temperature than we usually have in a full tropical fish tank, so if yours are albino
Corydoras paleatus, then the temperature being higher than they like would make them more sluggish and inactive.
So if you can share pics of the cories and tanks, then it may be something easily solved, and we can ID which ones you have if you share pics.
I've just recently got back into fish, and run into an old problem I've always had from my 20 gal to my 40 gal breeder. Tank has been up and cycled for years, just haven't been replacing fish until it got to the lone cory.
Is there still a single cory in the 40g then? I'd pop him into the 20g with the others then. Even if not the same species, I'm sure s/he'd prefer the company of the other cories rather than being alone, they're a very social fish, and the 20g isn't overstocked and is well filtered, so adding him wouldn't be a problem for the 20g.
I currently have a 20 gallon with 6 albino corys, 5 guppies, and a bamboo shrimp. Filters are 2 Fluval 30 HOB, with enough bio for a 40 gal (which is why there are 2 filters, don't want to chunk bio incase I set up the 40 again), and water parameters are good.
When you say water parameters are good, it's a bit too vague I'm afraid! Can you test for ammonia, nitrites, and nitrates, then share the numbers with us please?
My problem is no matter what I do, the cory's 95% of the time just sit at the bottom of the right side of the tank. I've had the tank in other parts of the room, moved the filters, removed a filter, lowered the speed/uped the speed of the filter, changed to a canister (hated that), uped the bubbler, added all the stress relief stuff, done melafix, primafix, treated for obscure diseases, nothing worked.
I can see how hard you've worked to try to fix it, and how it's frustrating! But better to avoid throwing in random meds. Some are helpful, some are needed at times, but some are snake oil, and can make things worse rather than better. Any time we medicate fish, it's stressful for them, so while it's tempting to just try everything, it's unlikely to be a disease, and can sometimes just turn a tank into a chemical soup and stress the fish even more, ya know? If you can't see visible signs of disease, then fresh, clean water is the best medicine in nearly all cases.
Not to mention it's expensive to buy all those products, and frustrating when it's not helping. But I understand it comes from a place of doing everything you can because you want the fish to be well and healthy, and you're willing to do anything to try to fix it! Let's target the problem, if there is one, so you don't end up with an empty wallet, and a fish stand packed with random half empty bottles of products that may be helpful, or may even do more harm than good.
They'll move around to eat just fine, but other than that they're lazy bums. The guppies and shrimp don't bother them either.
Any help is greatly appreciated, thanks!
You're not overstocked at all, and you say water parameters are good (would still like the numbers if poss) and obviously plenty of oxygenation and filtration. So just a few more questions to help isolate the issue, sorry for all the questions, but without being able to see the fish and tank, we have to probe a bit to see what may help.
This is the template the forum has for emergencies, but the same info is useful for mystery issues like this too. If you just copy/paste the template below, and fill out as much as you can.
What Others Need to Know to Help You
When posting a request for help can you please include the following info
1. Water parameters. (ammonia, nitrate, nitrite, PH, temp', Hardness etc)
2. A full description of the fishes symptoms.
3. How often you do water changes and how much.
4. Any chemicals and treatments you add to the water.
5. What tank mates are in the tank.
6. Tank size.
7. Finally Have you recently added any new fish?
You may cut and paste the template below and submit in your post:
Request Help
Tank size:
tank age:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:
Fish Symptoms (include full description including lesion, color, location, fish behavior):
Volume and Frequency of water changes:
Chemical Additives or Media in your tank:
Tank inhabitants:
Recent additions to your tank (living or decoration):
Exposure to chemicals:
Digital photo (include if possible):
