i've had the same problem with my basement system.. i've used nematodes and ladybugs with good results..right now i've got another outbreak of fungus gnats and aphids so it's time to order some more good bugs - i haven't had a day off this month so the my basement system hasn't been getting the attention it needs
i bought my first batch of ladybugs and nematodes from home depot.. there were around 1500 ladybugs in a pint i think..
the nematodes came on a couple of sponges...
ladybugs will hibernate in your fridge for several weeks so you don't have to release them all at once..
i also use DE (diatomaceous earth) and BT (bacillus thuringiensis)..
some folks swear by a "garlic+chilli+pepper" spray for aphids, but i've definitely had better luck with ladybugs
i'd avoid just about any other bug treatment, especially any that contain oils or soaps (surfectants)