Not Sure What To Do Anymore

[Najiran]

Tank size: 40gal
pH: 7.2 -7.6
ammonia: 0
nitrite: 0
nitrate: 20
tank temp: 80 deg. F

Fish Symptoms (include full description including lesion, color, location, fish behavior): one of my adults is kind of keeping to herself, seems to have what looks like worn patches on either side of her body behind her fins.

Volume and Frequency of water changes: 10-20% weekly

Tank inhabitants: if i found them all... about 12 platy 5 adults the rest fry all under 1inch, 2 yoyo loach, pleco, two immature angels, a few live plants.

Recent additions to your tank (living or decoration): the angels are new

Exposure to chemicals: none that i know of
 
My tank has been running for about a year and a half, and dispite a rough start my tank finally balanced out and has been running great for quite a while now. the thing is though i have lost a few fish seemingly for no reason. They just seem to become ill and fade away after having been healthy for several months they suddenly go off by themselves and then stop eating. this has happened 4 times so far and looking to be 5 soon the last one i tried medicating but it didnt do anything. I looked at the bodies and dont really see anything wrong.  I reaize my tank is a bit crowded at the moment, but even when there was only 4 or 5 platy  in the tank it was happening, and i plan on taking most of the fry out  along with an angel depending on what their genders end up being. All the other fish in the tank seem perfectly fine, They are breeding so it cant be that bad in there right? I appreciate any advice Thanks

 

 

[This Old Spouse]

Breeding is not a sign of a healthy tank, unfortunately. Fish will breed even in bad conditions, trying to keep the line going.
 
One thing I noticed is the temperature, which seems a bit high. Try dropping it down to 76 or so.
 
Also, make your water changes at least 20-30% weekly. And, it wouldn't hurt to add some more plants.
 
What kind of pleco do you have?
 
Can you post a photo of your tank?
 
Glad you joined our forum. Hopefully we'll be able to help.

 

[the_lock_man]

You said you had a rough start - would I be right in assuming that you established your cycle with fish in the tank, and they suffered periods of high ammonia?
 
I'm just wondering if your problems are due to the delayed effects of ammonia poisoning? Did the deaths start happening before or after you introduced the angels?

 

[N0body Of The Goat]

What fish have you lost to date? I could not spot that in the original post.
 
What is the fish that is being anti-social?
 
What are the dimensions of this 40gal?
 
As already said, regardless of this situation, I would turn the heater thermostat down so that is maintains ~76F (unless you know your "pleco" is a high end tropical species that must have >27C) and increase the water changes to 50% weekly.
 
It would also be worth doing a ~75% water change ASAP anyway, gradually refilling over ~24 hours (add similar temp water and let is naturally drop to the cooler ~76F).

 

[Najiran]

The Pleco is just a common one from the pet store other than that i don't know.
I've lost 4, two adult yoyo loaches and two red wag platy, the one that is acting anti-social is the remaining red wag platy from the original three i had gotten at the beginning but she has been very healthy since i put her in even when the others became ill, i guess it could be a delayed effect like you said, just seems odd that it would just suddenly bring her down like that after a year and a half.
dimensions of the tank are 36" L X 15" W X 16'' H 
I will try to get a photo up soon
I did the water change, hopefully she will improve (Other fish are happy and going about their business as usual)