Kind of looks like the waxy stuff aphids leave behind. Are your plants droopy and clawing often? Have you been fighting a mag deficiency the whole time?
If so and you have gnats as well be sure to check to soil for root aphids. They look very similar in mature form. Gnats fly lazily, while aphids dart around in straight lines or towards something in particular. They're very small and eat the shit out of your roots. I'm battling them currently. If you're not concerned about being organic and you're not in flower I suggest nuking them asap with something. At the point your plant is at you're about to have a serious population explosion within the next week or so if it is aphids.
If you're willing to use pesticides imidacloprid is a solid bet that's still somewhat "safe" to use. Meret 75 is one concentrated version available. Bayer and Monterrey etc make tree and shrub insect killers that contain it in smaller concentrations that are widely available at home depot etc. this is systemic DO NOT USE IT IF YOUR HARVEST IS LESS THAN 50 DAYS AWAY. I personally wouldn't suggest using it past maybe early week 2 I'm flower as it takes roughly 45 days to leave the plants system (although I've seen up to 60 supposedly). Another thing to consider is that imid is fine to be sprayed on fruits and veggies we eat but there's no testing for cannabis or inhaled substances that I know of so use your own judgement here on if you want to risk it.
There are stronger pesticides if you have a real problem but they have some pretty hardcore health risks in an indoor environment. Think along the same lines as inhaling eagle 20 causing fluid buildup in your lungs. Acephate would be the equivalent of an actual nuke to them but I'm not sure if be willing to spray something like that on my property, let alone in my house unless it were an absolute last resort. And even then I'd rather toss my harvest and just wipe the room down with a solution than spray it. Acephate is very toxic not only through inhalation but I've seen people on other threads who claimed to be exterminators saying it can also absorb through your skin. It's fetotoxic so if you have someone pregnant, soon to be pregnant or a small child i would avoid it at all costs. It's also believed to be neurotoxic with prolonged minor exposures and has a host of rather nasty side effects. However this may be a better option than relocation if the infestation is severe and persistent through all other options.
As with any other pest always dispose of any media bags stakes etc that had contact with these plants. Also try to disinfect and wipe down everything possible in and near your grow. Aphids are notorious for laying eggs and emerging again weeks after treatment because as with any bug they multiply exponentially until dealt with. I highly suggest if the infestation is bad that you hold off on your next grow if you're not perpetual and bomb or spray your room afterwards. Preferably a few times over a week or two just like you'd treat to kill hatching larvae in a plant.
Even if you're not organic I would consider brewing a tea of bennies to try to get the larva under control and to minimize the rotting root material they lay eggs near. Try to include the fungal spores used in botanigard, I bought OG Biowar Foliar and it seems to have worked well as a foliar spray and a root drench to kill juveniles and adults, while the bennies starved and ate the larva.
As an organic farmer you're more limited to the typical soaps/oils but I would 100% get a nice sized bottle of botanigaurd because you're going to need it. I'd rotate between that soapy water and clean water as sprays trying to clean the aphids off the leaves as they're stationary until completely done feeding and molting afaik.
Either way good luck and be sure to stay vigilant. From what i hear you'd rather have mites than root aphids.
