Dead Danio and other fish suffering

[DreamWave]

Hello, everyone. I'll start with the questionnaire first.

Tank Details:
Volume: 300 liters (~75 gallons)
Running for 6 weeks with a canister filter (Eheim eXperience 350) and a 350Watt heater set at 26C (78F)
The fish (44) inside are:
10 GloFish Tetras
9 (As of today) Glofish Danios
7 Neon Tetras
3 Plecos (Ancistrus, not sure of the exact kind)
5 Panda Corys
5 Orange Venezuelan Cory
5 Pangio Kuhlis

I also have 6 snails:
2 Ampularias
2 Melanias
2 Black Nerites

Maintenance:
I do a 30-40% change each week and vacuum the substrate. I always add SeaChem Prime to dechlorinate, SeaChem Stability to help the bio filter.
I add SeaChem Stress Guard when new fish are introduced and half a dose SeaChem Flourish once every two weeks for the plants.

*Parameters - Very Important
About Cycling: I added fish food and used a bacteria starter kit. The tank filled with white stuff, then disappeared on its own. I added the fish on the 10th day, but keep adding SeaChem Stability even now.
I test the water regularly with strips (JBL Test Kit) and with SeaChem pH Alert and Ammonia alert (long-term tests)

Ammonia: <= 0.25 ppm
Nitrite: < 0.5
Nitrate: < 10
pH: 7.2

Feeding
I feed them once a day, every night. I put in a few pinches of food (just enough so they eat it up in 2-3 minutes without any left). Then before going to bed, I add 6-7 pellets of algae for the bottom dwellers.
HOWEVER, three days ago I had to be out of town and used an automatic feeder, which added about double of what I would put in. It served food for two days and the fish got pretty big bellies. The next day I didn't give them any food and today I will feed them at night again.
The brand of food is Tropica
I give the fish frozen food once a week (two times so far)

Illness & Symptoms
I have had the fish (a GloFish Danio for 3 weeks). Three four days ago I noticed he is standing about 3cm (1 inch) from the surface and not moving much, like the other danios. Also, he kept breathing faster than the others (not much, but enough to notice).
After leaving town for 2 days I left the automatic feeder, which might have overfed the fish. After coming back yesterday, I noticed that the belly of the fish had red spots on it (you can see from the picture). I bought a "hospital" tank the same day, added 60% of the large tank water, substrate and elements from the large tank in it, moved the fish there and added SeaChem ParaGuard to treat.
I did a 30-40% water change on the large tank as well.
However, this morning, the Danio was dead. I took a picture of him, which I hope will help:
He was not injured upon purchase and was very active.

Explain your emergency situation in detail.
The danio is now dead (RIP). I noticed that 5 or 6 of the other danios now have red gills. Their behavior is normal and are very active - the gills are the only thing that I can see that is wrong.
Another thing I should mention is that one of my Plecos had a small white patch (around 5 millimeters) on his left side (between the eye and the fin) when we bought him 3 weeks ago. Yesterday I noticed that is has become larger (1 cm or half an inch). It looks like a piece of cotton. In the center of it there is a tiny wound, which is red.
This Pleco is now also in the hospital tank, being treated.
I also added SeaChem ParaGuard to the large tank, because I was worried it might be contagious. I plan to add it again tomorrow and then stop (because it is prophylactic ).
I also plan to keep the Pleco in the hospital tank for at least 2-3 days after the white patch disappears and his wound heals.

Overall issue:
I am worried that this might be contagious and that I am not doing the right thing to prevent an outbreak. I actually paid 3 times the fishes' cost for the hospital tank and water additives, but it doesn't matter. I love my fish and I want THESE to be in my tank.
Do you have any idea what exactly killed my Danio ? Am I doing the right things ? What else should I do ?

Thanks in advance.

 

[ProudPapa]

1. I'd start with another 50% water change. I can't promise it will help, but it can't hurt.
2. I assume your source water is chlorinated, and you're adding something to neutralize that? The additive you mentioned may do that, but I'm not familiar with it.
3. You listed your water parameters above, but when was it tested to get those results?

 

[DreamWave]

Yes, I will keep doing water changes every other day.
SeaChem Prime removes chlorine and heavy metals in the water.
Those tests were made last night, before the first water change.

 

[TWiG87]

I would also look into getting a good liquid test kit for testing your water. The strips can be ok, but a liquid test kit will be far more accurate.

 

[DreamWave]

I would also look into getting a good liquid test kit for testing your water. The strips can be ok, but a liquid test kit will be far more accurate.

Does that mean the symptoms and picture look like ammonia/no2/no3 poisoning to you?

 

[JimC22]

Your Danio looks like it had septicemia. Most likely caused by secondary infection from ammonia exposure. You say your other Danios have red gills which is a symptom of ammonia exposure. What has happened is your tank may not have completed the cycle before you added fish. Or you did not have enough beneficial bacteria (BB) to support the bio load created by the fish added. Did you add all these fish at same time or over time?

Right now your test shows elevated ammonia and nitrite. Those results indicate you have a cycle still ongoing. The most important thing now is to do water changes to keep ammonia and nitrites levels at or below what you show, ammonia and nitrites at or below 0.5 ppm. This will allow the cycle to complete and reduce the exposure to your fish.
You will want to do this until you see both ammonia and nitrites reach zero for 24 hours.

The water changes may need to be done daily.

The important part is to watch your water parameters and keep the ammonia and nitrites down so they do not stress and hurt the fish. Watch them closely for any secondary issues.

Also, can you post a pic of the Pleco? It could be a couple different things and the picture will help identify. Sounds like it may be a fungal infection or columnaris (bacterial infection). Need to identify so you know what med/meds to treat the fish with.

 

[ProudPapa]

Yes, I will keep doing water changes every other day.

I meant now.

 

[JimC22]

Yes, I will keep doing water changes every other day.
SeaChem Prime removes chlorine and heavy metals in the water.
Those tests were made last night, before the first water change.

Your using Prime - good. You can add Prime to your tank. It makes ammonia safe for the fish. It does NOT remove ammonia, but for 48 hours the ammonia will not harm them. Ammonia is still in the water which you need to feed the BB and complete the cycle.

So every other day you need to add enough Prime to treat the amount of water not being replaced during the water change.

 

[DreamWave]

I see that everyone is worried about the aquarium cycle. I will buy a liquid test tonight (in about 3 hours) and post back the more accurate readings.

 

[DreamWave]

I just bought a SeaChem Ammonia,NO3 and NO2 tests and did them.

Ammonia = 0
NO2 (nitrite) = 0
NO3 (nitrate) = 1

This is after the 30% change from yesterday and the added SeaChem Prime

I see no issues with the water conditions.

Also, the pleco that was in the hospital aquarium died. After taking him out if the water, a piece of his skin fell off, where the white stuff was (pic attached)

Any other ideas? Treatment for the other fish?

 

[MEWaters]

sounds like overstocked and not a full cycle; too soon
keep up on frequent water changes and keep testing / watching

 

[JimC22]

That's a good test. Nitrates are lower than expected with the amount of fish in the tank. Whether the cycle was complete or not, you most likely had an ammonia spike in the tank after adding the new fish as the BB was not yet adjusted to that size of bio load. Add the event where you were away and suspect the fish were overfed. The the extra food added to the bio loading, there-by increasing the ammonia. Without water testing you'll never know. The red gills of the Danios is a good indication of ammonia exposure.

It looks good now after all the water changes.

If it was me I would continue water testing, making sure the parameters stay good. Perform water changes to keep the water pristine while the Danios heal. Hopefully the red areas disappear quickly. Watch them closely for any secondary infections. You will want to act quickly if something come up. Come back here if you need any assistance to deal with it.

Sorry you lost the Pleco. It will be hard to say what it was, but based on what you said, it was already sick when you purchased it. If it had been Columnaris your chances of successfully treating the fish where not good. I've never been able to save one, even when caught early.