Plant problems, 1st grow, Need help

[WannaBeFarmer21]

Have a small indoor set up with a friend of mine who seems to think he knows everything yet has no answers to help fix thus issue we are having. Currently have a 4x4 tent using HGL 225 R spec lighting, good circulation, temp and humidity are on point. Use happy frog soil and he also mixed in Stoningtin Blend organic & natural growers mix. Am watering every 3 day. Have 3 autos that are about 2 weeks into flowering and 3 photos 27 days old (white widow and diesel) running lights 18 on 6 off. Noticed a few days ago the leaves on the autos have rusty colored spots and "burnt looking tips" and my photos the bottom leaves are turing yellow but the tops look good. My partner says we do not need to feed the plants the soil we have is enough but after some research am thinking there may be a nutrient issue (nitrogen??) of some sort just not 100% sure so am looking for help advice on how to fix my queens up. Lastly ph is around 6.5.

 

[TripsRabbit]

Looks like maybe a calcium deficiency. If it were mine I would use calmag and fertilizer every 2nd or 3rd watering. The dirt has some nutrition but not enough for the whole grow unless it's super soil.

 

[WannaBeFarmer21]

You think its the same for both sets of plants?? Is there a specific brand you recommend?? I was thinking the same about the dirt that we are gonna need some sort of nutrients for them especially after seeing some of these pics plants the same age and twice the size. Thanks for the advice.