Sick cory cats

Question
QUESTION: Hello,
I have a 35 gallon freshwater, planted aquarium, it has been going for about six months and is completely cycled showing no ammonia or nitrites and nitrates between 20 and 40.  This is a molly tank with one male sailfin, four female sailfins and 8 neon tetras along with three wonderful, playful cory cats (I think they are called "peppered").....until two weeks ago.  One of my cats died unexpectedly and now I am watching the other two very closely, they seem lethargic, hang out in my plant (water sprite) and are not running around the tank like normal, I have not seen them eat either.  

Recently all of my molly's had "litters" of babies and there are probably 30-40 fry from 1-6 weeks old.  I have upped the water changes and have included frozen baby brine shrimp in the feedings for the molly's.  I don't know what could be causing my cory's to feel sick.  

I do have a hospital/isolation tank that is 2 gallons but hesitate to stress them by moving them to a new uncycled tank.  Any help would be greatly appreciated.
Thank you,
Christa

ANSWER: Christa,

Sorry to hear your fish aren't doing well. In my opinion, your tank is overcrowded.  My suggestion to you is to buy a min. 55 gallon tank, move all the fish except for the Molly fry into the new tank. Be sure to cycle the new tank first, using the water you remove from the 35 gallon tank when you do a water change, ( this water contains necessary bacteria required for proper cycling) as well as conditioned water.  My first question to you is, How long have you been feeding the Molly's baby brine shrimp?(and what is the brand name of the shrimp) I also need to know how often you do water changes and what percentage of water do you remove?  What temperature do you keep your tank at? and  What are you feeding your Tetra's and Cory's?          
If you could provide this information, we may be able to figure out why your Cory fish are sick. I would also like to mention how very important it is  to have your hospital tank cycled and ready at all times. Once again, using the water removed from the 35 gallon tank when you do a water change.  

Looking forward to your response.

---------- FOLLOW-UP ----------

QUESTION: Hello,
Thanks so much for such a prompt response!  I plan on removing all of the fry and donating them to a local fish store, also moving the male sailfin into my 75 gallon angel tank to prevent further spawning.  Is my tank still overcrowded at that level?  I also have a 27 gallon bowfront that only has four platys in it and a pleco so there is plenty of room there as well if need be.

I am feeding frozen cubes of baby brine shrimp, I don't know the brand as I threw away the overwrap (sorry).  I have been doing this for three weeks once a day, in addition I am also feeding a variety of flake, crisps, nori and dehydrated shrimp throughout the week.  Generally I do two-three feedings a day for the fry.  I use Prime for water conditioning during water changes, water changes are done weekly of between 25-50% depending on levels, if it looks like nitrates are getting high, I will add an extra one during the week.  These fry are playing havoc with my nitrate levels!  My temp is kept at 78 degrees and my ph is around 7.2 - 7.4 (I don't adjust it once it comes out of the faucet, too much chance of losing fish due to PH issues).  I am wondering if the cory's would be better off in my angel tank or if they are too small.  The angel tank has five angels, two valentine cichlids (gypsogymnophagus) and 8 black skirt tetras, plus one albino pleco.  I am wondering if the cory's aren't getting enough of the right type of food or if the molly fry are just too busy and are stressing out my cory's. Thanks for your help with this!  
Thank you,
Christa

Answer
Christa,

I think that the moving of the fry will make a huge difference as far as tank issues. Also, I wouldn't feed the fry only frozen brine shrimp. You should add micro worms ands vinegar eels and flake type food for the fry too. I think the 2 to 3 feedings of brine shrimp for the fry are whats messing with the cats. The fry are being over fed and and the cory's are eating whats left on top of what you are feed them. I would either move the cory's to the hospital tank, or get the fry out. At 6 weeks, they are ready to be sent to the pet store. You might be able to get either cash for the fry or credit to buy supplies. That is what I do with my Betta fry. After the fry are gone I would do a 50 to 75% water change in that tank, and make sure you vacuum the gravel good. Leave about 1/2 inch to 3/4 inch of the gravel untouched since the tank needs some of the bacteria that is in the gravel. If after all this is done, and your cory's are still not ding well let me know and we can figure out what to do next. Once the fry are moved and the male, the over crowdedness should not be a problem.