Red Dots on Guppy - Any Ideas?

[Twood]

Hi everyone. I noticed that one of my guppies has a red spot on it, and seems to be in bad shape. Below are the tank details, its a heavily planted 40 Breeder that I am colony breeding livebearers in. The tank has been up and running for 4ish months, started with a couple guppies and Platies and they have been breeding up a storm. Any ideas what the red dots are on this guppy and how I can treat it. The other fish seem to be fine, although I lost one other female guppy about a week ago that looked completely healthy, but I did notice after it died that it had a red spot on it as well. Thanks for any help!

Tank Size - 40 Breeder

Lights - on a timer set for 10 hours a day, Stingray

Filters - two Aquarium Coop sponge filters

Inhabitants - colony of red dragon guppies (maybe 30 or so), colony of Platies (maybe 10 / 15), two juvenile bristle nose, snails

• pH - 7.8
• Nitrates - 10
• Hardness - 150
• Nitrite - 0
• Ammonia - 0 
• KH/Buffer - 80
• Water Temperature - 77F

Here is a photo

Edited April 29, 2022 by Twood
Adding Photo

[Fish Folk]

Oof… looks externe, bacterial. QT and treat. I’d probably reach for E. M. Erythromycin / Maracyn first… 

[Twood]

Thanks so much, appreciate the help!

[Torrey]

I second Fish Folk, especially looking at the tail damage. What does your tap water test at, and how often do you do WC?

[Twood]

I do water changes whenever something tests out of spec, but no fewer than probably every four weeks. I added the Med Trio on Friday, and am going to let the fish soak for a week. I am not sure what my water tests at out of the tap. I checked it before I set up, but should check again. I know its no nitrate, nitrite, ammonia or chlorine. Can't remember pH and buffer. Ill check it out and let you guys know how treatment goes. The fish in the picture already seems to be doing better two days into the treatment. Fingers crossed. Thanks again for your advice.