Well Established Tank Disaster

[kashifg]

Hi,
im still recovering from whats happened. i have/had an established malawi mbuna setup for around 8 years. I bought 6 adult mbuna from a private seller a week ago, all seemed ok. But then 2 days ago, a few fish died, this morning woke up to find every single fish has died except for maybe 3-4, which also looke very poorly! (around 30 mbuna, all pretty much adult size)

Now i have never had this problem in the past, since keeping the fish. So i am completely puzzled, what would have caused this. No changes to maintenance routine or equipment, this is as it has always been. Tank is a Juwel Trigon350, with an external Eheim 2128.

I am considering changing the setup and not going with malawi's again, but a simple tropical community tank. I need some advice as far as stocking again. Considering the outbreak of whatever it was, what should i do before I introduce fish again. Can i assume that the bacterial filter is all still in place and that i can introduce a full community of fish straight away?. Should i clean the existing filters (internal & external) as well as drain all the existing water?
the tank setup was full of ocean rock all across the back wall on both sides with coral sand as the substrate. Now i think i will need to replace the coral sand as this will not do a community tank any good? But I'm not sure about the ocean rock, if this can stay or not?

Still depressed about the whole thing, but trying to see if i can pick up and get it all going again with a change round of fish at the same time.
Appreciate any advice from the community.

 

[Juggler75]

Could it have been old tank syndrome? I've never experienced it but you might want to read up about it and see if symptoms fit.

Ocean rock has buffering capabilities the same as coral sand, so may not be suitable for some communtiy fish, but it will depend on your future stock, your target pH, your tap water values etc.

 

[creeker]

Could it have been old tank syndrome? I've never experienced it but you might want to read up about it and see if symptoms fit.

Ocean rock has buffering capabilities the same as coral sand, so may not be suitable for some communtiy fish, but it will depend on your future stock, your target pH, your tap water values etc.

I agree with Juggler. No disease takes fish down that fast. It had to be water conditions. I have seen tanks crash down into the 4's on ph before.

 

[Fishy friend2]

Were they bullying eachother or did the new fish have a disease when you bought it, or has anyone been messing with your tank, and I agree with juggler

 

[kashifg]

Had a read up on 'old tank syndrome', and this doesn't quite fit i think. Everything was fine up until i introduced the new fish a week or so ago. There was some bullying going on when the new fish were introduced, but to be honest this is the nature of mbuna, and it happens in established tanks, let alone with newly introduced fish and i have always had this when introducing new fish over the years. there was no sign of disease on the new fish from what i could see.
so moving forward, how should i handle the existing water/filters?
i have a test kit, which is years old, so i'm not sure if that's even worth using to take some tests?
thanks for the input.

 

[creeker]

100 percent water change and a new test kit.

 

[kashifg]

ok managed to pop to local shop and picked up some tests.
Ammonia & nitrite both at 0. PH is 7.6
Nitrate is sitting in between 40-50mg.
The few that are left look like they are happy..ish, the fish shop suggested they would be happy to take them back in.
Should i wash my filters out in tap water, or better to leave alone?
Is my PH ok for a community tank?

 

[eaglesaquarium]

Why would you want to wash the filters in tap water? If you were going to do that I would think just going with new filters entirely would be better. Washing in tap would pretty much kill the bacteria and leave you with an uncycled filter, but potentially diseased media.

7.6 pH is fine for some fish, but not others. A liverbearer community would be very happy in that pH.

 

[kashifg]

Normally i would never consider washing any filter/media under tapwater, but considering what my tanks gone through i'm just not sure what to do, which is why i'm looking for advice.
Going on whats been suggested so far, i'll leave the filters as they are, do a 100% water change. then its out with the ocean rock/coral sand.

will look for a new substrate, and then look at getting some new fish.

 

[creeker]

Yeah. I agree. I would keep the filter as is. It sure doesn't sound like it was any disease. I feel for you. Many years ago I lost a whole tank of saltwater fish when my well meaning mom sprayed cleaner on it.