Fermentation issues and fruit flies

I'm looking for some opinions regarding my latest batch of beer.

About a month back, I brewed a porter. OG 1.060, SG 1.020 when I racked to secondary. I used one of those 8 gallon fermenters from BMW that don't have the tight o-ring sealed lid. When I opened it last Sunday, there were tons of fruit flies beneath the lid and at least one that seemed to be in the beer. I tasted a sample and the beer tasted ok, but held off on any other additions.

The gravity issue might be due to setting my old analog controller to 58F to keep the chamber temp at 70F max. I plan on testing the porter again when I brew tomorrow. If it tastes ok, should I just add some of my S-04 starter to try and drop the gravity if needed? I also intended on adding vanilla and cold brewed coffee at some point.

What do you guys think about possible infection? Also, has anyone else had trouble with this type of fermenter? All I can figure is either the lid or airlock somehow let all these fruit flies in.

Fruit flies can definitely lead to problems. I don't think I would invest much more in it from what I've read it will probably go south(luckily I don't have first hand experience with it).Was this secondary an 8 gallon container if so what was the batch size?

Infection is a real possibility, I would think.

Keg/bottle and drink as soon as possible. Fruit flies are literally dripping with acetobacter, which turns alcohol into vinegar: it's a defense mechanism. There's no sense in adding to the beer. The clock is, in my very humble opiniong, against you, especially if your fermenter wasn't air tight: acetobacter only works in oxygenated environements.

Be also aware that if acetobacter has taken hold in the beer, anything plastic that touches the beer might become irremediably tainted since the bacteria will happily thrive for long periods of time in scratches or cracks in equipment, even after a careful cleaning and sanitizing regimen has been employed.

If you have a problem with fruit flies, you might want to set up a few traps around the house and make absolutely sure that there's no spilled wort or anything else left to fester/ferment in your brew room or around your equipment. Fruit flies are attracted by anything that ferments.