Corys Dying, Unknown Cause

Tank
What is the water volume of the tank? 10gal
How long has the tank been running? Since April
Does it have a filter? Aqueon Quietflow 10
Does it have a heater? Don't know what brand but it works very well
What is the water temperature? 78-79
What is the entire stocking of this tank? 1 albino cory, 1 betta, many snails (1 assassin)

Maintenance
How often do you change the water? Every weekend, but recently I've done a change in the middle of the week to fight worms (assuming I have both planaria & detritus ?? long & thin white worms that get up to a centimeter, but also some very small fat ones that I can barely see with my eye. my betta eats both which worries me)
How much of the water do you change? 20-30%
What do you use to treat your water? imaginarium betta conditioner
Do you vacuum the substrate or just the water? As much substrate as I can !! id say I keep it pretty clean.

*Parameters - Very Important
Did you cycle your tank before adding fish?
What do you use to test the water?
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.

Ammonia: I don't have test strips yet because my local store was sold out last time I went, but I got it tested last week at petco & the guy said it was "fine" so :/
Nitrite: 0
Nitrate: less than 20
pH: 6.5 (used to be a stable 7 but it settled at 6, ph up treatment boosted it but also supposedly killed my first betta)

Feeding
How often do you feed your fish? in the morning & at night
How much do you feed your fish? betta gets 2-3 omega one pellets, cories used to get a bit of a pleco algae disc that id cut up into a small piece for them, but since there's only one & she isn't eating much I don't know what ill do tonite.
What brand of food do you feed your fish? omega one & hikari
Do you feed frozen or freeze-dried foods? I have freeze dried blood worms but they are NOT my bettas primary diet. treats only.

Illness & Symptoms
How long have you had this fish? about a month & a half ??
How long ago did you first notice these symptoms? two weeks (when the first of my second cories died0
In a few words, can you explain the symptoms? lethargic, not eating much, slowish darts to the surface for air. more frequent than I think is normal for cories, I can't tell.
Have you started any treatment for the illness? no, I was going to get salts from a friend & possibly parasite guard tomorrow.
Was your fish physically ill or injured upon purchase? no, not that I could see. but I'm assuming the second cories all had parasites from petco. I can't remember what they were housed with but it made me very concerned.
How has its behavior and appearance changed, if at all? again, lethargic, not eating. reread symptoms.

Explain your emergency situation in detail.

I'm very new to fish keeping. This is my first tank, & I was issue free for a month, but now I've hit some huge problems. Run down: Tank was running for months, then in late June, I saved a betta. Originally I was planning to get shrimp but I felt bad for him. Got two albino cories along with him from Petco. Everything was healthy. Then one of the cories got injured & died (no parasites or anything, the sponge on my filter slipped & hurt her because she got stuck on in )

I got 3 new albino cories the next weekend, also from Petco. I've realized now I didn't really have room for them, but they were babies & the tank wasn't overstocked, but since then each one has died. Tonight the last of that batch of cories has died. The original betta has died as well. Petco told me to raise the PH of my tank with PH Up, which is what I suspect killed him. I have another betta rescue I got yesterday in there now, because my test kits always come back stable & I assumes the tank was safe. I am now suspecting parasites. The cories have been dying for absolutely no reason. My last cory is lethargic, as all of them slowly had become. The don't eat much, go to the surface pretty often for bottom feeders (though I don't know how often is too often). I know they're nocturnal so I assumed their laziness came from daylight, but I've checked on them at night & they seem just as lethargic.

I suspect an internal parasite. I don't have any of their poop because my gravel kind of sucks. I would prefer to do heat treatments or something similar before I try medicine because, last time I tried medicines & chemicals I watched my bettas fins fall off until he died the same night.

If I am doing some bad practices, PLEASE tell me !!!!! I care about my fish so much, but I'm worried I'm a terrible owner. They've just kept dying recently, there must be something I'm doing wrong. I try to avoid Petco as much as possible, but the best fish stores are a decent way away from my house, & so I don't have a chance to go to them nearly as much.

Again, If my practices are wrong, or I am doing something wrong, please tell me.

 

I apologize for the long post, thank you to anyone who can help !

 

update this morning: woke up to find my betta on the bottom of the tank with labored breathing. within 20 minutes hes died. he had what almost looked like swim bladder issues (floating weirdly, only swimming a little) but I know I don't overfeed him. he then started spinning in circles / doing flips (I had him in a small cup) then fell to the bottom & stopped moving. I just got this fish 2 days ago. he showed no symptoms at 1:00 last night, now its 7:30 & hes gotten what I can only be POSITIVE is a parasite. I only have my one cory left. will be going back to petco today to return him along with some rude remarks to the man who smart mouthed me about how my ph was killing them. absolutely not ph. I had no issues with my tank until I bought the second batch of cories. also will not be going back to petco after this.

thought I could slip by on their bad practices because everyone knows they suck. boy was I wrong. please avoid petco if you are a hobbyist. go somewhere else or don't get fish. ive watched some of the most brutal deaths of my bettas & cories so far. its not worth it.

 

another note: my cory is INTENSELY lethargic. she has gotten so much worse. I poked her & thought she was dead, but she moved. very delayed. she will probably die as well. I don't have hope that she will live.

in this case, if all my fish are dead & all that's left are snails, should I still try to remove parasites ?? will they move to my snails next ?? I have no idea what kind of internal parasites I have.

I believe within the next few hours, she will die as well. basically, should I still treat for parasites ???

 

It sounds like your second Cory's came with something that effectively messed up the health of your fish, illness possibly

6 to 6.5 pH is average so isn't wildly bad for most fish species

I am guessing that you did not quarantine the second lot of Cory's before introducing them so if they did harbour anything, that is how you ended up with your fish passing away

I think you will have to clear the aquarium, sterilise it and start a new cycle from scratch and then buy fish from elsewhere. Start small & hardy like Tetras once the aquarium is back on track. A 10 gallon is a tad small for a full school of Cory, they like minimum 6 preferably 8+

Above all else try not be too disillusioned, this happens to everyone and anyone who says they have never lost fish for a variety of reasons is probably telling fibs

Start from scratch on your cycle after sterilising the aquarium, find a reputable supplier for your fish and just keep trying...

 

It sounds like your second Cory's came with something that effectively messed up the health of your fish, illness possibly

6 to 6.5 pH is average so isn't wildly bad for most fish species

I am guessing that you did not quarantine the second lot of Cory's before introducing them so if they did harbour anything, that is how you ended up with your fish passing away

I think you will have to clear the aquarium, sterilise it and start a new cycle from scratch and then buy fish from elsewhere. Start small & hardy like Tetras once the aquarium is back on track. A 10 gallon is a tad small for a full school of Cory, they like minimum 6 preferably 8+

Above all else try not be too disillusioned, this happens to everyone and anyone who says they have never lost fish for a variety of reasons is probably telling fibs

Start from scratch on your cycle after sterilising the aquarium, find a reputable supplier for your fish and just keep trying...

alright, thank you. a fresh start will be good ! ive learned a lot in the past month or two with actually have live fish. I didnt think to quarantine them, but of course that was an error on my part.

again, thank you. this has given me hope ! ill remember next time to quarantine & look better for symptoms.

 

Its not always possible to quarantine new fish, you have to have a fully cycled aquarium hanging around for that, so don't beat yourself up just cos you didn't have a second aquarium for that purpose

When you buy fish you kind of hope that the supplier has done the necessary quarantine and health checks before the fish go on sale, sadly not all of them do and then well meaning people like yourself buy the fish and run into problems once home

When looking for a fish supplier try to find someone who actually guarantees the fish and who states and can prove they are fully quaranteened before sale. I am lucky in that I have an online supplier who does exactly that....however that doesn't always mean the fish are healthy, one of my new ones died overnight last night, but at least you can either take the fish or a photo of it to your supplier and they will replace or refund for it

There will never be absolute guarantees of success with fishkeeping but as you become more experienced and know what to look out for you will be able to read the signs that your fish are telling you and be able to act on them accordingly

I would absolutely start again, don't ever give up or lose heart on this pastime cos once you have your established aquarium they are truly a joy to behold and all the heartache and expense getting there will be worth every penny

 

Pagoda is absolutely on point!
Best of luck and never be afraid to ask questions!