Lost A Cory, Others Not Themselves

[aRKaNity]

Greetings, first time posting here. I'm sorry to start with bad news but I lost a Julii Cory today and I'm worried about the rest of my school.

Background: I have a 20L tank that has been set up for about 2.5 months. I ran the tank with no fish, but some live plants for about 5 weeks and saw what I thought was a cycle. I added six of the Corys and a Bristlenose Pleco. They've been apparently doing pretty well, but about 2.5 weeks ago I went through nitrite spike that I assume was the real cycle. Nitrites registered >5.0 for about 72 hours and then dropped to 0 where they've been ever since. After the nitrite drop I added three drawf gourami: a standard, a powder blue and a honey sunset. Ever since then the nitrate levels have been difficult to control. I change about 33% of the water weekly, although during the nitrite spike I changed 50% every other day or so.

Water quality: PH 6.0. Ammonia varies between 0.50 and 0.25. I have never been able to get it down to 0. Nitrites 0, Nitrates between 40 and 80 ppm. I have a moderately planted tank with Amazon Swords, Java Fern, Water Wisteria, a Marimo moss ball and some grasses. I also have a largish piece of bogwood.

My Gourami appear to be panting rapidly, although I am unfamiliar with the breed and this may be normal. They respond well at feeding time and seem energetic. The Dwarf and the Powder Blue Dwarf have been sparring for territory, but don't seem to have been injured at all. the Honey Sunset is about a third the size of the other two gourami and does well, but hides a lot. He does not seem to be panting as noticeably.

The Corys are my main concern. They are lethargic even at feeding time. three of the remaining five seem to be better, but two will not move away when approached by the other fish and seem mostly to just hover on the bottom. I understand this breed can play dead, but after a real death I am concerned.

Any help, advice etc would be appreciated.

 

[snazy]

Your tank is heavily overstocked and the ammonia is killing them, your filter isn't coping with the bioload, so basically they are being poisoned by the highly toxic ammonia. Honestly, you need to rehome all your stock, none is suitable for the size of the tank.
Or get a bigger tank, 100L minimum for what you have already, and a bigger filter suitable for a bigger tank. Then put both the current filter that has gone through some cycling and the new filter. Eventually, the second filter will pickup some of the bioload and will level the ammonia and nitrIte to 0. Until then, large water changes(not just 50% because that removes just 50% of the toxins, so if nitrIte is 5ppm, 50% will leave 2.5ppm in the water which is still lethal to the fish, so apply common sense)
This is the only way to save your stock and if you go this route, you need to do it urgently before the fish die.

 

[aRKaNity]

As stated in my original post nitrites are at 0 and the ammonia load is within safe ranges at 0.25 ppm to 0.50 ppm, although 0 would be ideal. Everything I have read states that this is not an overstocked tank. Keep in mind that a "20L" is 20 gallons, not 20 liters so about 75 liters and at this stage these are juvenile fish, so I have about less than 11 inches of fish in that 20g tank.

I am running a MarineLand Penguin BioWheel 150 which is rated at 30g.

This evening everyone seems quieted down, so I'm hoping it was just the stress of the 50% water change that I was seeing in the fish. I will let them rest for 24 hours from the change and do another change tomorrow.

Sorry about the mixup about the liters vs gallons.

 

[snazy]

Oops, I thought the tank is really 20L

You didn't menion gallons...
Ammonia is safe when it's absent, which means 0! Any other level is toxic and that's the problem with your fish. Your filter is not coping with the bioload anyway it seems or you have something rotting in the tank.

Edit: I do 50% water changes on all my tanks weekly and it never stresses the fish, so that's not your problem. Do daily water changes to keep ammonia/nitrIte as close to 0 as possible but you need to figure out what's causing the spikes.

 

[Baccus]

If the fish are lethargic and gasping the other thing that springs to mind is lack of oxygen in the water. What temp do you have the tank set to and what type/ species of cory do you have? Different corys like cooler water than strictly tropical fish. Warm water holds less oxygen than cool water thats why in my Queensland summer heat I have airstones running in my tanks to help with extra surface agitation and quicker heat exchange.

 

[MrsM]

OP stated the tank was 20L in first post, i gasped too snazy......

NO ammonia is safe! waterchange!!

i also thought cory breathed air, so they wouldnt be lethargic due to lack of oxygen??? would they?(im still learning too)

 

[Baccus]

They do come to the surface and gulp air but if they are already lethargic and the tank is deep they can have trouble getting to the surface. My corys rarely do the mad oxygen dash but are always busy bustling about the sand on the hunt for food.

 

[aRKaNity]

Thanks for all the input folks. The 20L designation is the model of the tank, a 20 long which measures 30" x 12" x 12". It's shallow enough that even the two corys who still seem to be struggling this morning are able to go to the surface for air. Seemed I read somewhere that this is not necessarily part of their respiration routine, although it can help but they use the air as ballast? May be wrong about that...

This morning the rest of the tankmates all seem much better. I will follow yesterday's 50% water change with another water change this afternoon. Would it be unsafe to do another 50% or should I stick more in the 25% range today? I will test levels prior to the change and then in a situation like this I would probably re-test a couple of hours after the water change. Any thoughts?

I think I am my own worse enemy. I suspect I've been overfeeding since I added the Gouramis. They eat all I give them but I was reading that if they get more protein then their bodies need they excrete the excess, some in the form of ammonia and some as protein waste, which of course turns to ammonia as it decays in the tank.

I'm always careful to vacuum the gravel at each water change and usually will do the open areas plus move a different ornament each time to get the area underneath.

Thanks for your interest and suggestions. Hopefully I can get the ammonia under control before I lose anymore of my fish. Do you have any thoughts about the ammonia lock additives you can purchase at the LFS? I hate to add anything artificial to the tank, but if these are effective at reducing the toxicity of ammonia, I might have a go.

 

[snazy]

The ammonia is way more dangerous than large water changes, so for the time being I would stick to 50% and larger, as much as it needs to bring the level to near 0. Just make sure it's dechlorinated and temperature matched water and the slower you poor it in, the better. Once you get the ammonia under control, the corys should recover from the good conditions.