Lost Tom Selleck tonight.

[NegativeLogic]

Sorry to hear about your losses.

I'd really recommend getting a test kit for yourself if you can. I test my water at least once a week or so (unless I'm worried for some reason) just to make sure all the parameters are good. It's also good if an emergency happens because you can very quickly start ruling things out (or confirming them).

In terms of cause, have you made any changes to anything you do recently? Adding or removing chemicals, anything you add to adjust the parameters of your water etc. It would probably be good if you could explain your entire maintenance and feeding routine for everyone.

If you see anything odd on the fish themselves (like lesions) then pics would be very helpful too.

 

[BELLUM]

I would do a water change anyway. It can't hurt anything.

Oh and stop naming your fish. All the ones i name seem to die.

 

[imafloormatt]

I do a 1/3 water change once a month or if I notice the water is murky. I feed them mostly tetramin tropical fish crisps every day but once or twice a week I give them frozen blood worms. The newest thing in my tank is a common Pleco but I added him several weeks ago. I did a water change about 3 weeks ago now and dechlorinated as always and added a little bit of some beneficial bacteria boost but I only did that because I cleaned my canister filter and did a water change on the same day but I got my water tested a few days after and nitrite and nitrate were at 0 and PH was at 6.9-7 ish if I remember right. Other than the bacteria boost, I didn't add anything out of the ordinary. Is it possible that they ate themselves to death? I did notice that both of the fish that died suddenly got fat a few weeks ago but I started feeding them less when I saw that.

 

[Chrisk-K]

I got my water tested a few days after and nitrite and nitrate were at 0

Nitrate=0 means there was no beneficial bacteria. Unless you provide numbers from a current water test, we can only guess.

 

[jpappy789]

I agree with Chris...is your tank planted though?

I would recommend getting a liquid test kit (API is what most people here use) for yourself so you can make sure you're getting accurate and current readings.

 

[kevinb120]

Not sure I would go a full 5x dose of Prime right of the bat. I have done 2 to 3x but that seems like a lot.

Well, that would be for an ammonia or nitrite spike over 1.0ppm(not yet cycled tank), but it's hard to tell what the heck is going on without a test kit.

You just can't do this hobby properly without a reliable way to test water. I started this with the LFS testing and strips, once I got the API master, everything quickly got fixed, and stayed fixed...

 

[sorberj]

Here's another question. You said the fish got real fat right ahead of time....did their scales start poofing out a bit (sort of like a pine cone)?
Additionally, when you cleaned your canister filter, how did you clean it?