Please Help! Fish Dying!

[Kez0okm]

Hi everyone,
I could really use some help.
So my husband has a 125 lt tropical tank. He's gone away with work and left me in charge so I'll put as much info as I know. The tank had 3 gourami, 4 clown loach, 2 plecko and 3 penguin tetras.
This morning I woke to find one of the gourami dead and one of the others doesn't look well at all.
I have checked the ammonia (0)
Ph was 7.6 so I added recommended amount of pH down and nitrate level was also fine. There is no evidence of white spot or parasites (they had calimanus? Worms last year so I know the signs), no dropsy and I've been doing weekly 10% water changes and 3 weekly filter changes.

I've been so careful as I desperately didn't want to kill the fish and I'm completely out of ideas.

Does anyone know what I may be doing wrong???

Thank you.

 

[Akasha72]

Hi and welcome.
 
Okay so there's quite a lot here that needs help with but firstly lets sort out why your fish are dying. How are you testing the water? Is it with test strips or with a liquid drop test?
There is some key here with the water changes and the filter. Firstly the water changes arn't really large enough. You really need to increase to 25% weekly to keep nitrate low. You say that this is 'fine' but you've not given the actual figure so it would be good to have that if you can please. Can you also check the Nitrite too and let us know the figure there too.
 
As to the filter - never change the media unless it's absolutely falling to pieces. When you do your water change keep some of the old water back and just give the media a swish in the old tank water. This is all you need to do, just give it a little wash and pop it back.
 
Next problem .. never mess with the pH with these pH altering products. All that happens is it rises or lowers the pH dramaticly and then when you water change it alters again. This results in the pH swinging wildly and that is more dangerous for the fish than just leaving things well alone.
 
Next I need to tell you that those clown loaches are going to grow to around 18 inches long and so your tank is not going to be big enough for them in the long term. To keep clown loaches you really need a very large tank of around 6 to 8 ft long.
I'd also be concerned about the pleco's. Some pleco's remain small at around 6 inches in length (the bristlenose for instance) but the common plec can attain 2ft long and a foot wide. They've rightly gained the name of 'tank buster' because they grow enormous and there really is no place for them in the home aquarium. If you can post some pictures of the pleco someone will be able to identify them (it's not always easy to ID them as there are loads of different types) and we can let you know if they are okay in your tank or if they are likely to 'bust' it!
 
Now the penguin tetra - lovely fish but they need some more friends. These fish are a shoaling species and live in large groups. To see the best of them you need to consider increasing their number to at least 10.
 
Hopefully that's helpful to you. If you can give us the numbers for Ammonia, Nitrite and Nitrate we might be able to see what has killed the fish. It's highly possible that the gourami died of natural causes. One fish death isn't always something to panic over but if we see a lot of deaths one after another then that's the point to consider something isn't right.

 

[Munroco]

I'm not sure if you mean you are changing the actual filter media or just the cotton wool like stuff that goes on top. If its the first like Akasha says, don't change it, if its the second then you will have done no harm. While your PH is a little high for these fish, that isn't an issue atm.