Black spots under leaves

The spots look like some sort of pest on first glance. They could be mites or aphids as I know ladybirds like to feast on them. It would be best to start a IPM or integrated pest management system into your grows if you want to continue growing long term. This can be putting stuff in the water to kills things in the medium to spraying the plants in veg so they have some extra defence to the critters that want to eat them. If we had more focused shots of the spots we could help identify it better, My guess is still mites and I do see some white flys on them as well. They are little pieces of shit, but much easier to kill then the mites. Given you are in flower the treatment options are limited but not zero. soap and water then washing the plant in the shower/outside is an option to get rid of most of them. Then at harvest doing a bud washing will help get rid of the letovers. Calcium deficiencies are visible from the top of the leaves not the bottom, pests hide on the bottom to avoid predators. FYI: We will not be notified of any reply or tag [@] in the questions part of the website, if you need to reach out with other information use your DM "direct mailbox" in the bottom right hand corner of the page. it looks like a little paper airplane icon. Best Of Luck!