I've read that using just coco coir I should ...

The sensi bloom a and b has all you need in it.

Hi there. I have only ever grown in coco and have a bit of experience using multiple water sources. The only time I supplement with Calmag is when I was using RO water. I use coco specific nutes and my tap is around 180ppm so it works perfect for me to go without it. If you do end up needing to supplement with calmag, be cautious with your dose. Going to high of a dose will cause lockouts of other macro snd micro nutrients as well as salt build up. If you use calmag, make sure you feed to sufficient runoff frequently to keep your root zone healthy. If you have tap water 140+ ppms and use a good coco specific nutrient at the proper amounts, you shouldn't run into deficiencies. Most "deficiencies" are actually caused by poor root zone pH conditions which is usually from over feeding. Tl;dr Usually only if using water with base ppms under 120 and definately RO water. Mileage may vary based on mineral composition.

Hey there, If your using well water it most likely would contain it in the water. That's why you may not be having much of a problem they look pretty healthy from the pics👍. If you do chose to add a Cal-Mag product start with a lower amount than what they state probably start at like 1/4 strength if that. A lot of the products contain Nitrogen and other nutrients in them there are some that have it separate but most have a combination there are ones that are better in veg and some that are better in flower due to one having nitrogen and the other have potassium it's things to consider. Happy Growing!!

Why don't you do one grow with Calmag and one grow without it and see which is best for your girls. I used to grow in coco and never used Calmag.

Hi, most mixed calmag products contain nitrogen, and you are right to have some fears to overfeed your plant. You can get calcium and magnesium as single fluid products. ( canna) If you use this one you dont have to worry about overfeeding your plant. Calcium and magnesium keeps your plant healthy and helps the photosynthesis.