Problem With Drain Flies In Aquarium

I'm having a problem with drain flies in a 40 gallon aquarium. The tank has a aquaclear 70 and I let the level drop a bit (about 2 inches from the top) to increase agitation at the top. I just can't seem to get rid of these guys. I don't actually see the larva but occasionally I spot the pupa. Usually in the morning I have 30 to 50 adult drain flies and I can quickly vacuum them up (they can't out run the vacuum suction. I've been doing this for about 8 days and I'm not sure I'm getting ahead of the curve. I've cleaned out the filter twice by rinsing the material in tank water (in a pail which I then flush) and the actual filter itself in tap water and wiping it clean. I also wipe the rI'm around hte tank 2 or 3 times a day. Given that hte larva should be .1 to .2 inches long I would think I would see them but I don't - and I guess the fish aren't interested in eating them....
-
any suggestion how to get rid of them without harming the fish.
(tank population is 6 kuhli, 1 bristolenose, 1 panda, 1 upside down cat, 2 swords, 6 cardinal tetra and live plants - 3 amazon swords - growing very well - one java fern - starting to put out new leaves, 1 minI anubia - not doing well). Will likely add a ehiem 2217 canister filter next week to increase flow.

 

the eggs and larvae could be in the substrate as well. try to vacuum as much as the substrate as you can.

you could try the sticky fly traps that you hang up to catch the adults as they fly around.

 

I had not thought of this - do the larva require oxygen; from pictures they seem to have a breathing tube which would suggest they need to be near the surface ?
-
I've been using sticky tape where I see them landing (outside the tank); it doesn't really attract them but it will grab em when they land.

the eggs and larvae could be in the substrate as well. try to vacuum as much as the substrate as you can.

you could try the sticky fly traps that you hang up to catch the adults as they fly around.

 

not sure on the larvae.

I just read that you can get a cup with some apple cider vinegar and a drop of dish soap (break up the water surface tension), cover it with cling wrap, poke a few holes in the cling wrap and set it in the area the flies are. they'll be attracted to the apple cider vinegar and drown in it.

 

Doesn't work. Tried that. Also chatted with a friend who had problems with drain flies (in a drain); they tried the apple cider stuff and it didn't work for them either.

not sure on the larvae.

I just read that you can get a cup with some apple cider vinegar and a drop of dish soap (break up the water surface tension), cover it with cling wrap, poke a few holes in the cling wrap and set it in the area the flies are. they'll be attracted to the apple cider vinegar and drown in it.