Reddit mentions of Ecological Labs AEL20036 Microbe Lift Mosquito Control Aquarium Treatment, 2-Ounce

First thing, soggy soil is a haven for fungus gnats. There will be tons of suggestions about letting the soil dry out more inbetween waterings. It's valid, but using a product and that practice may help reduce chance of re-infestation.

Mosquito dunks are good - my only qualm was they're a pain in the ass to break up and looks messy sitting on your soil surface.
I recommend this:

http://www.amazon.com/Ecological-Labs-AEL20036-Mosquito-Treatment/dp/B007UTE55A/ref=sr_1_7?s=lawn-garden&ie=UTF8&qid=1426531941&sr=1-7&keywords=microbe+lift

A drop or two every week should take care of any issues with gnats.

Here another variety of BTi that I've been using.

http://www.amazon.com/Ecological-Labs-AEL20036-Mosquito-Treatment/dp/B007UTE55A

I'm rockin the microbe lift, yellow traps, and the mosquito bits. Seeeeeee yaaaaa gnats :D

This: http://www.amazon.com/Ecological-Labs-AEL20036-Mosquito-Treatment/dp/B007UTE55A

It's BTi, which is the same as Gnatrol, and Mosquito dunks and all that.

But it's cheap, in liquid form, and totally bacteria based and safe.

I use it with every watering in every res, along with hanging yellow sticky traps to catch adults, and so you know how things are going.

It works very well and is easier to use than mosquito dunks in my opinion, and more effective.