A big hello to all as I am new to this forum,

In the last two months I have started to keep Goldfish. Our tank is 16'' in length, 8'' in width and 9'' depth. It has an electric powered Flulux filter and I change 40 - 50% of the water each week. The water tap is treated with Aquasafe to make it safer for the fish. The fish have been fed flake food (although today I have brought pellets after reading on this site that they may be the better option) and the kitchen in which they are situated receives plenty of light.

Originally we purchased two ''red'' goldfish (Mario and Luigi!!) from a local pet store. Everything seemed fine for a month or so until I noticed some black substance on the inside of the tank (on the glass) and also that Mario had developed a black mark above his mouth. I cleaned the tank and the black substance and again everything seemed fine for a few days. Mario showed no ''odd'' behaviour and was eating well. However, one evening I discovered Mario dead and lots of the black substance on the inside of the tank again.

I cleaned the tank completely and Luigi seemed well enough and showed no signs of illness. A week or so later I purchased two more Goldfish, one red - Wario, and one for which I don't know the name of the type (short, predominantly white and a bit ''pot bellied'' - Princess Peach. Again all seemed well for three weeks or so but, having returned from a week in Rome (in which the fish were fed two to three times a day as usual and the tank cleaned twice), I noticed a lot of the black substance on the inside of the tank, and hours later found Wario dead.......I cleaned the tank completely but 24 hours later Princess Peach died (although she had some sore looking red/scarlett marks on her underside).

I have attached a photo of the black/brown substance. It's not the best quality but you can make out the substance reasonably clearly.

I would be so grateful for any help, advice or knowledge imparted. Is the black substance related to the deaths?? Is it a bad batch of fish from the Pet Store?? Am I doing anything wrong?? Please let me know. I'm find it quite upsetting that they keep dying .....plus, I'm running out of names from the world of Mario

Thanks in advance

Pablo

I hope your fishie gets better Im sure one of the mods will help you soon.

You could call your next fish Yoshi lol. But make sure that the others are healthy before getting another one and be sure to quarantine it first.

Hi Pablo and welcome You may want to post as much info from the white box at the top as you can, this will help the experts give you some advice.

The first thing that jumps out at me is that your tank is far too small for one goldie, let alone 3 or 4. Fancy goldfish need a minimum of 10 gallons each and single tailed goldfish (commons, comets, shubunkins) need at least 15 each, since they can grow to enormous size in a short period of time. Overstocking such a small tank means your fish are swimming in their own waste and it is poisoning them. I think even if you did a huge water change every single day, you would still be teetering on the edge of disaster. Any way you can upgrade? Even a large rubbermaid container would be fine.

As for the black stuff, I have no idea what that could be. Is it really black or is it more brown? It could be brown algae? I'm really not sure about that. The black mark on the fish may have been ammonia burn from the excess waste in the water.

As far as everything else, you are on the right track. Your water changes are a good volume and a good frequency (for when you are not overstocked anyway). You are trying to improve their nutrition, which is great. Variety is great! Try some softened veggies (microwave them in some tank water) to help with digestion issues. Peas are a great addition to goldfish diet - make them like I described above and pop the insides out of the shell before you feed them (make sure they are no salt added!). Pellets are better than flakes, but make sure you soak them first if they are the floating variety. If you can upgrade Luigi to at least 10 gallons and keep up everything else that you are already doing, things may turn around. Clean water is the best medicine for a fish!

Good luck

Imtammyo has just responded with pretty much what I was about to type, your tank is a 5 gallon tank, which is really too small for the amount of fish you're trying to keeping, -this will be the most likely candidate for the reason why your fish keep getting sick/dying. -The black marks on the fish do sound like ammonia burns.. -Have you read the section on cycling on this board, it's great information that will help answer your questions about the 'toxicity' of the water, and how a good setup will help you avoid this...

Koko's note on cycling..

And I was also guessing the same as Imtammyo, the 'black' stuff on the tank, -is it more brown than black? new tanks often get a breakout of brown algae over the first few months, -this isn't actually an algae but single celled organisms known as diatoms. -Although unsightly they are not detrimental to the fish. The bloom of the brown 'algae' is self limiting and as your tank matures the brown algae will eventually disappear, -you can reduce the speed of growth of the algae by keeping the water changes up, and scrubbing down the surfaces of the tank during water changes.

-you mentioned you have attached an image of your 'black' tank, -I can't actually see the image.. -can you post it again? this would help confirm whether the 'black' stuff is just brown algae.

-Don't let this turn you off keeping goldies, most newbies who come to this board have similar problems that you are finding, -if you have the space/funds to have a larger tank, this can be a great hobby to get involved with. -and your 5 gallon tank set up can be used for a different type of fish like a beautiful betta (siamese fighting fish)! -Be warned tho', it can get addictive!!

Pablo, how are things going?

Any improvement?