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· Registered
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Discussion Starter · #1 ·
I have a few questions about my tank. It has been running since Feb, 21, had fish in there since Mid-March. In the last 2 weeks or so I have had a whole lot of fish death and I can't work out why at all. I have looked all around the internet for good info but can't seem to find anything that relates to what is happening in my tank. Thought I might send you a message to see if you have any suggestions.

My tank is a 500L (132 Gallon) with two SunSun 304-b filters. I also have a sponge filter. I have regular play sand as substrate along with holey rock and driftwood for the fish to find shelter in. There is also a wavemaker at one end of the tank. I have two 300w heaters operating on angles at either end of the tank.

My stocking list is as follows:

2 x Bristlenose Catfish
3 x Mono Sebae
2 x Cyrtocara Moori
4 x Labidochromis Caeruleus
2 x Paratilapia Polleni
1 x Metriaclima Pyrsonotos

I understand it probably isn't best to mix all these fish and I am wondering if this would have a major impact on the health of the fish within the tank.

My parameters have been fairly stable the whole time the tank has been up and running. I have started recording these in the last few weeks since the fish death.

Date PH Ammonia Nitrite Nitrate GH KH
3/5/21 8.2. 0 0 5 12 7
10/5/21 8.2 0 0 10 12 8
17/5/21 8.2. 0 0 10 13 7

I do a 50% weekly water change every Monday. I haven't got a python water changer so at this stage I am just using a garden hose feeding directly into the tank. I add Prime (Full tank dose), Cichlid Lake Salt and Malawi Buffer (both replaced water dose) to the tank with every water change.

Most of my fish still seem to eat well, until they are very close to the end where they lose their appetite. I feed them a mix of Hikari BioGold and Excel mixed with garlic guard and vita-chem. All of the fish seem to hover near the bottom and appear to be working their mouths or gasping almost continually. I have attached a photo of a fish who also has red markings above the mouth and near pectoral fins. It has been like this for upwards of 2 months now and in terms of personality it seems to be the happiest fish.

I am at a complete loss as to what could be the issue with the fish dying. I have been checking for any signs of disease, and aside from the red markings on one fish, I can't see anything. I would really appreciate if you have any tips or suggestions as to what may be causing issues in the tank and what I can do to help keep the fish alive. I really want to be a successful fish keeper.

Sorry about the length of this message but I wanted to pass on as much detail as I could. If there is any other information, I can give you to help I can let you know anything you need.




· Administrator
40,927 Posts
I have never seen red marks on a fish like that, but then I have never had a combination like that in my tank. In the absence of any other evidence, I would isolate the fish with the red marks and see if he improves away from the suspect tankmates.

What are the dimensions of your tank? What was your stocklist before the deaths?

· Registered
1,732 Posts
Red markings could be a bacterial infections: ... -blotches/

Not sure why the blotches would only be on one fish, but if other fish are dying...

disclosure: I've not personally seen this nor treated with the instructions in the link, just remembered reading it recently and passing along in case it can help you.

Also not related to your illness but I see you're in australia I'm guessing it's pretty warm where you are and that's why you're able to fill directly from a garden hose? Anyways just wanted to caution you about your heaters. Just 1 of those 300W heaters is likely more than enough for your tank and could potentially raise the water temp too much if failed in the on state, which is common. IME, a 150W heater was enough for your size tank to raise the water temp 14 degress F above ambient room temperature if fully on. I'm putting my tank in the basement where I might need the temperature rise to be ~20 degrees F and I'm worried a single 300W is going to be too much.

· Registered
351 Posts
I agree with Rhinox. This is almost certainly a bacterial infection based on the lack of outward signs and the speed with which it kills. Make sure that both UV sterilizers are on in the filters. If they will eat, I'd mix up some medicated food and feed them a broad spectrum antibiotic like Maracyn Two if you can get hold of it.
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