their are 5 instars to a root aphids life
the first 2 are very small
the last 3 can develop wings if they need to find new enviroments, they are hearding insects meanign they group together and eat and migrate to new roots.
you will see the larger 4th and 5th instars looking like mature beetles , still small though.
they can be brown, red , black, white... but they are all in the family of root dwelling aphids that using piercing sucking habit of eating.
i would use a desiccate insecticidal soap to clean everything, like M-pede, then use a drench or sprench to contact kill them at the root zone, pyganic 5.0 or a spinosade BV product. If you use Pyganic make sure to wash it out and that its has a very low amount of petroleum distillate in it, or you will kill your plants(do not use MAXX)
you can then inoculate your media with enthrpogenic/bacteria fungus like PRF 97 or grandevo.
all of these insecticides have different modes of action and you need to alternate them every 3-5 days to beat their reprodcutive cycle.
aphids will react to your treatments they will try to hide and migrate.
Do applications sytemically so that they cant migrate as you open doors and go into new areas.
Aphids can give birth to already pregnant young ready to give birth instantly after, these are prolific pest. dont slack on applications , once you have them under control(this is the most likely scenario) you will need to continue some treatments.... Grandevo and PFR 97 both have secondary modes of action and are OMRI, and so is M-pede(which acts as both a desiccant and a cleaner and repellant and is also plant and roots safe)