It sounds to me like you did all the right things...

The corydoras are most likely very young and the stress of coming from supplier to LFS to your tank was just too much for them. Did you purchase them soon after they had received them?

 

“I did a temp acclimation for 20-30min”

If you only did temp acclimating you only did half the job. PH shock and osmotic shock (shift in water hardness) are actually worse on the fish than the temp part. Open bag, roll over edges so bag stays open, clip it to edge of tank. Then take turkey baster and remove some water bag, squirt in waste bucket, replace with same amount from tank, no more than about 10%, 50% LFS told you is way to much at a time. Lather, rinse, repeat every 10 min for next hour. Little tiny betta cup of water your just doing tiny squirts.
@Discusluv hit on a big one too. The double whammy. They just went through a big transfer shock shipping to store, then you come along same day or next and don’t do a full, slow water parameter acclimation your just asking for trouble. Learned this from a little local mom n’ pop fish store guy we use to have here, always had neatest fish, but he would not sell you a fish until 2nd day after he got them in.

 

...to my newly cycled 10gal tank on Saturday..(

How long has the tank been actually up and running? I would bring them back, try to get a credit and let the tank mature and grow out some. That's always the safer route.

 

Thanks everyone!

I'm on Day 33 since setting the tank up, I used a live nitrifier and pure ammonia to cycle the tank (plus the hitchhiker snails and a surprise fry that came along with the plants). As of Day 27 I had stable parameters of 0ppm ammonia, 0ppm nitrite, 10ish ppm nitrates, I added the fish Day 30. My LFS tested my water yesterday when I brought back the first dead fish, with the same results (0, 0, 5-10). They also tested the water again today when I brought back the three dead fish today (0, 0, 5-10) and tested the PH which came out at 7.4. The amano shrimp, nerite snail, and surprise fry are all doing well.

I had another lengthy discussion with the lfs guy who was very happy with everything I've done. The cories were young, and all from the same new shipment. I know they have a waiting period before selling new fish, but I don't know how long that waiting period is (at least 24hrs as I overheard someone wanted to buy a fish from a blackout tank yesterday and the manager said they wouldn't be ready until today). He replaced them with two paleatus cories, hopefully they do better. Esthetically I prefer the pygmy cories, I really wanted a little group of them, but the bigger ones are fun too. If they do well I'm still happy.

I am also trying the longer acclimation suggested by DaveKS with these guys. I've done this way in the past too (I've been out of the hobby for a few years, but had tanks before), but searching about acclimation in the last few weeks as I was getting ready for fish, I've been reading pros/cons of both. I thought about making an actual drip system, but I have my dedicated baster for the tank, so I'm using that now (they acclimating as I type).

Thanks for the advice and suggestions. I was so excited to finally get fish in after trying to do everything right. It was a bit of a blow that they all died.

 

Plop and drop is my method of acclimation and has been for the last 30 years. Plop bag with fish in tank, scoop out of bag, drop in 15 minutes later. You want to get that fish out of bag as soon as possible- ammonia accumulation is the primary problem with acclimating fish- not osmotic shock.

Most of my fish are wild and come from very soft water: geophagus, Altum Angels, biotodoma cupidos, corydoras, African tetras... and many more. I get most of my wild fish from the Wetspot in Portland. Their ph is in the low 6's- mine is 7.4. No issues, no problems acclimating the most sensitive of fish.

They all get introduced into my aquarium as quickly as possible- 15 minutes to temp acclimate.

 

Discusluv, that's what I was finding more people recommending when I was searching the last few weeks. I've had success with that in the past, so thought I would do it that way with the pygmy cories. Tried more parameter acclimation with these two new peppered cories, fingers crossed. So far one is snuffling around, exploring and being a great little cory. The other one is still hiding in my dense plants. I hope they do well!

 

As soon as you can, get at least 4 more corydoras to go with the others. They do not do well in small groups- the more you have the more you will see them.

 

I got a group of 15 from Wetspot. Lost one due to cory curiosity and getting stuck on the filter intake. The other 14 are doing great, but were super shy until I got a larger dither fish. They seem more comfortable with something swimming above them.

 

I'm not sure my 10gal can support 6 full sized peppered cories and a betta, but I have a 20long waiting in my basement as my next project that I'll be starting soonish.

I was thinking of adding the peppered cories to the big tank once it's up and running (I have an extra sponge filter running in my 10gal to help speed it along when the time comes), and then trying pygmy cories again in my 10gal, I really do want a little group of them. I think I'll add another two of the peppered cories (for a total of 4) maybe next weekend if everyone is doing well and then the betta the week after (I'm postponing the betta for a bit as I have a surprise fry at the moment from some plants that I want to grow out a bit). I'd have at least 6 peppered cories in the big tank when the time comes.

Guess it's all part of the fun seeing where this hobby takes you!

 

Good plan. Six will be fine temporarily in 10 until move over to 20 gallon- they will actually be more comfortable. Just do a 25% water change on the 3rd day and the 6th day after adding other corydoras to help the bio filter catch up to new bio-load.

 

So good news, the two new peppered cory’s made it through the night. They were looking great when I left for work this morning.

So you think it would be better to have six peppered cory’s in the 10gal temporarily? I have a bunch of extra filters, should I put another one on? Would make it easier to jumpstart the new tank too...

Would I need to increase my weekly 30% water changes to handle the overstock?

Thanks!


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Yes, if you are planning on another tank, adding a filter to your existing aquarium will jump-start that process.

I do think it is better to have a maximum number ( depending on tank size) of corydoras together at one time than a couple. But, of course, you must at the same time stay on top of your water parameters. Anytime you add more fish to a current system you need to think in terms of added bio-load. It will take a certain amount of time for the bio-filter to accommodate the new fish. A new setup- one that is under 3 months, will take longer to establish the needed beneficial bacteria to match an increased bio-load. An established bio-filter, above 3 months, will be quicker to match.

To be safe, do a water change on the 3rd day, and the 6th the first week. Use Prime as your dechlorinator when do water changes, if possible.
I always do 50% minimum water changes weekly on my aquariums. Actually, I have discus in 3 of my tanks, and do 2- 75% water changes weekly- but, that is not necessary in your case.

So, I would recommend 50% water changes in the 10 gallon starting the 2nd week on- until transfer the corydoras to a larger tank.

 

Did you have them in a quarantine tank for at least two weeks? Old school here Dr. Innes (can be found on Amazon from the 50's and more salient then most)

One "matured" a tank (let the bio bugs do their thing) over months (see it takes patience the natural way) Fish were slowly introduced to allow the bio bugs to adopt. In my day there were no heaters! or complicated filters. That said one learned to study the basics. (I was at the library often way before the www)

Water changes as some suggest at 50% are horrific for fish. They are Osmotic creatures and every water changes give them great GREAT shocks to their immune and other systems.


As well, in the wild corries (of all species) are in groups in the hundreds if not thousands. All such schooling species need to be thought of as One - a ten gallon is way to small for them in reality.

I had 100 gallon tanks when I lived in NYC that I did partial changes (from the bottom where the crud settles) once a week (about 1/5) and topped it off with heat/ph/kh filtered water (done in a huge garbage tub as NYC was toxic) I used as small air filter hose line to dribble the new water in through out the day. No sudden shocks.

People - imagine someone takes you off planet earth and plops you down somewhere else. It is a shock. May not appear right away but these sudden drastic changes eventually do harm.

 

Much respect to Dr. Innes- I have his book on my shelf. But, we have learned a few things about water since the 50's, and large water changes in the aquarium ( in most situations) are not a "metabolic shock" to a fishes system. That is- like you admit- an "old-school" methodology--- Aged water was better water, small changes, no shocks. Sure, you want to check your water report to see what your dealing with; but, for most- the benefits of 50% water changes weekly ensure that a fishes immune system is maintained.



I understand your reluctance for technology- Ive been in this hobby for 30 years and yearn for when things were simpler. But, just because filters and heaters have become more powerful and digital does not mean people dont know the basics of water chemistry and fish health.

 

Small fish are delicate and often die for no obvious reason. Especially when new.

 

So it's been a week, and the two bigger peppered cory's are doing great. I'll be hitting up the LFS tomorrow to get some more. It'll be awhile after that before I add in a betta, I still have that surprise fry that I want to get bigger so hopefully it doesn't become a snack.

I am hoping to start getting the 20gal tank set up maybe tomorrow. It needs a huge scrub first, and it's been cold and rainy forever now (a few snowflakes still last weekend!), but is supposed to be dry and warmer tomorrow so I want to take it outside and go to work on it. Once I get that up and running and cycled, I'll move the cory's over.

I have noticed that the three amano shrimp I bought last weekend are also gone. I found the remnants of one a few days ago, I'm assuming the snails made short work of them once they died. I've found amano's to be tricky in the past, some seem really delicate, and some seem to be super hardy and live forever. I did find someone kind of local who breeds them, but they're about 1.5hr away, not sure I want to make the drive.

But slow and steady, I'm in no hurry.