Issues With My Tank

[Kuroku]

Tank size: 15L 15g!!
pH: 6.5
ammonia: 0
nitrite: 0
nitrate: 50

Tank info: Contents of the tank as per my signature, including 4 large-ish plants. Tank is cleaned once a week (makes no difference to the Nitrate levels though... ). Fish are fed once a day with flakes, once a week pellets and 1 algea tablet with the exception on one day during the week of no feeding. Tank light is switched on at 12pm, switched off at about 9pm.

Tank itself is 2 years old.

It started with a Corydoras mysteriously vanishing from the tank. Being an armoured catfish I thought there was nothing in there that could eat it... So I checked behind the tank and all round the floor in case it jumped out when I was cleaning, but no (unless one of the dogs got him... ). There was no smell to the water and I had all ornaments out and all plants checked through since I was water changing at the time anyway. Another Corydoras became ill and died out of the blue, it was swimming erratically and died overnight... After which the other two Corys had developed fungus, which I promptly treated and the treatment cleared the fungus completely. Their eyes had also swollen up, but after a further water change the following week, this too cleared up.

The Plecostomas* which I had intended on taking to an LFS then became ill himself, he's stopped eating and just sits at the side of the tank (My 2 Chinese Algae Eaters died the same way a year ago) and he's very thin. He doesn't even poo very much...

There is also a heavy accumulation of Algae... Black algae to be exact... This is a first for the tank... It's on all the ornaments, plants, glass and filter... There's not much light in the room and the light is only on for a minimum of 9/10 hours a day.

And now one of my Black Neons is poorly... The tail is pale on the outside and bright red on the inside and appears to be a bit stiff. I have no idea what this is...

*The pleco is two years old and only 6 inches long. I had been sold a 'Red Gibbiceps' (adult size 10cms) according to the lfs I went to... >_< Not knowing any better I bought this guy and learned a while later that he was a Sailfin Pleco! I had planned to upgrade my tank anyway but lack of space and money cancelled my plans... I worry about giving him to a fish shop incase he dies too on route to the lfs or they won't take him because he's ill...

Also, I don't know if it's relevant, but my old Betta died a couple of months ago, this was due to a Tumour.

I hope you can help me!!! This has never been a problem in the 2 years I've had the tank until now...

 

[Puffdaddy]

Sound like a water quality issue may have started this, do you use strips or liquid tests. Your nitrates are high meaning you have excess nutrients in the water (the cause of the algae). Also your tank is overstocked a 2 year old Sailfin Pleco only 6" is grossly stunted and will likely have problems the rest of its life. Unless you get a bigger tank or remove all your fish and restock properly, all your fish will get diseases and die. Sorry if this sounds harsh. But a 15ltr tank (4gl) is hardly a tank and the only fish that can thrive in it are a single Betta or very small fish such as Dwarf Puffers or various shrimp and snails. I'm sorry that this has happened to you, sounds like your lfs has no clue about the advice they are giving (typical).

 

[Kuroku]

Thank you for your advice. I wasn't aware that the pleco was a Sailfin when I got him... Which is a shame really...

I'm guessing that the first thing I need to do is rehome the plec. If he's placed in a home with a much bigger tank will that improve his stunted growth? Or is he likely to have problems regardless?

Edit: I'd like to add that I'm dumb with units and I don't have a 15l tank... I DO however have a 15g tank!!!!! >_< Apologies for the confusion...

 

[Puffdaddy]

I'm sorry to inform you but the damage has all ready been done on the Pleco, I'm not quite sure what it's health would be like in the future if properly housed. And I would say the Pleco is the cause of all you problems. These are the steps you need to take to return your tank to normal. Must be done in order.
1. remove the pleco ASAP
2. remove as much algae by hand as you possibly can
3. give all fish a Methylene Blue dip (to aid in ammonia & nitrite poisoning)
4. do 75% water change (to remove extra nitrates)
5. do 15% water change everyday for 5 days. (to minimize nutrients so algae will die off)

Black algae is a pain to control so do some reading up on it. You can either add an Siamese Algae Eater(Crossocheilus siamensis), there are commercial products, also hydrogen peroxide is know to be effective, among other remedies.

 

[Kuroku]

I see, thanks for your help.

I'll see if any lfs are willing to take him in.

Thanks again. Next time I'm avoiding plecos of any sort. I can't afford the risk of mislabeling once again!