Looks like fungus gnats to me too.
It's the curse of indoor growers everywhere. For a grow that is a single season crop then I'd look for organic solution but for a long lived tree that can only accumulate trivial amounts of toxins in it's juvenile stage, I'd just use an ordinary insect spray - Mortien, black and gold - whatever.
Just spray the room and don't directly spray the plants, spray it close to them but don't paint the leaves with it. Repeat at least twice in the next few weeks to get the larvae when it hatches.
I do mine in a tote or bucket, I use it like a fumigation chamber and never spray directly onto the plant. After spraying I put a board over the top of the tote/bucket and let it sit for about 30 mins. Not much will survive such a fumigation except the larvae - hance the need to re-treat in a week or so.
Get all the plants out of the room and spray it with poison of choice, fumigate the hell out of it and shut the door for a few hours and wait it out.
From my observations fungus gnats have two main sources for infestation. The first one is potted house plants and the other vector is introduced through fruit and vegetables that we bring home, onions being the main culprit. The bastards live in the loose layers of onion's skins. So put them in a gnat proof setup, my onions go into a stocking and I always find heaps of dead gnats in that stocking.
I see you are using Rockwool - an excellent choice. If it's pre treated properly it can be the possibly the best medium there is for many plants (not all). Many or possibly even most people don't know how to pre treat rockwool and never have optimum results when using it for a growing medium.
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How to pre treat rockwool
I'm very surprised how many commercial growers don't understand this, a simple ion sample should be indicative enough for any commercial hydroponic producer to understand this but many growers ignore this basic information we determined in the early years Rockwool culture. Dutch growers had it refined within 3 years after the introduction of Rockwool, but the rest of the world has struggled to understand this fundamental principal of Rockwool culture.
Rockwool (untreated) has a property where it buffers the initial pre soak PH 1 full point higher than the first soak. I believe some of the grodan brand is pre-treated but most brands are not.
So if I have plant that uptakes nutrients optimally at PH 6 the Rockwool has to pre-soaked at PH 5. After the the pre-soak the Rockwool will typically settle at 1 full PH point higher than the pre-soak, so a PH 5 pre soak will result in a working PH of PH 6.
Many people will do the first wetting at system PH (PH 6) with the normal nutrient solution, which the Rockwool will buffer 1 point higher (PH 7) and the system will always hover around that mark forever (far from optimal). Pre treat your Rockwool and you will never look back. the plants will be able to utilise (almost) all the nutrients they come into contact with and thrive like never before.
Nice plants Shadow!
