Pleco bacteria causing fin rot? Possible?

[Spiritofthesoul]

Whose keeping fish? You or those people?
Screw their impressions, you decide what you want to keep.

I would recommand apple snails since they generally prefer cooler water

 

[Redearsunfish]

I recommend doing it the way I do it, the old fashioned way. By hand with an algae magnet. seriously.

 

[MonsterMinis]

That makes sense. Thank you for the input.

For a little background on the situation: he had 2 angels & 3 goldfish (I have no idea of the sizes but he said he'd had 1 of the GF for 5 years) in a 10 gallon tank, then came to my shop (I have a small pet shop/LFS) and bought a 4" pleco (I did not have the background on his tank at the time).
About 2 days later he called saying that his goldfish were all hiding down in a corner of the tank, the opposite corner from the pleco and were acting slightly lethargic, so he wanted to bring the pleco back because of how the GF were acting. I let him bring the fish back and returned it to the tank it had been in prior. About 4 days after he had brought the pleco back he called to say that his GF had, what he thought was, fin rot, were still acting lethargic and sitting in the corner of the tank and he believed the pleco had caused it because "he had read that plecos have bacteria in their skin that would cause infections in GF". He asked for medication for it and because I did not have anything on the shelf to sell, I gave him some of my own Maracyn-Two to use. But the infection was to far along in his fish and he ended up losing them.
Basically I'm looking for information that I might not have about plecos causing infections in GF and to figure out if this is somehow my fault.
I do not sell fish out of sick tanks and I clearly mark any tank that has fish (ANY sick fish not just when all the fish in the tank are sick) that are ill.
A note on the pleco that he sent back; it was put back into the tank it was in (with its fantail and long-finned GF buddies) before going to that gentleman's home and I have not had any problems with any of the fish being sick. I have had ich crop up but I am ascribing that to the changing weather (I always see ich crop up in the spring and fall) because it did not happen till a week after the fish was returned.

Well, so much for a little background, ha. But thank you for any thoughts that anyone has.
And if you believe I am to blame, please let me have it and let me know what I should have done. I make an effort to take care of all of my animals and sell them to responsible homes but there is ever more to learn.

1. 2 angels, and 3 goldfish in a 10 gallon is insansely overstocked to begin with.

2. because of this overstocking to begin with I'm guessing the guy also rarely if ever does water changes. IF so it's unlikely he's doing more then 20% once a month.

3. Because of 1, and 2. THe water chemistry is likely compromised. Even if the tank is cycled.

4. Adding a common pleco, other then whats already been pointed out on an aggression level. They are poop factories. So this would comrpomise teh water quality further.

5. Extended poor water quality leads to a variety of bacterial infections in fish. It's like getting a paper-cut.. then rubbing feces into it. Literally. The tiniest cut is going to get infected.

My suggestion. Don't carry common plecos. There are many smaller species of plecos and algae type eaters available that do a far better job then commons do, and will not give you so many headaches.

a 10 gallon tank isn't large enough to house a single goldfish.. let alone 3 and a pair of angels.

 

[Diamund]

Thank you to everyone for your input. Here is a progression of info in this case.

I have had a total of 3 conversations (so far) with the customer regarding his tank and have had the opportunity to see the fish that died. It was definitely (in my opinion) a water quality issue.
They originally had 2 goldfish (a 7inch -nose to end of tail- LF GF and a 5inch fantail GF) in their tank (which "had been fine for years"), then added a 2inch Pleco & a 4inch Comet, when the GF killed the little Pleco they came back and bought a 4.5inch Pleco. When the GFs started hiding in a corner away from the Pleco they returned the Pleco and got a 4inch fantail GF to replace it. Then all the GFs started getting sick. (I can go into symptoms if anyone wants more info)
It sounds to me like they had a tenuous balance going with the 2 GF and then when they started adding and changing up all the fish the combination of added bio(hazardous)-load and unfamiliar bacteria caused the water quality and health of the fish to crash.

Spirit: It is someone else keeping the fish. I don't have a problem with them keeping that many fish UNTIL they force the bio-load off balance and then try to blame me for the problems they are having.
Thank you for the Apple Snails suggestion.