HELP! Help with lower yellow leaves and brown spots on leaves.

[Hellogrowers]

Hi all.

It is my first time growing, my plants have entered week 5 and I have a problem with these brown spots which are still coming back on new leaves. I only water once every week as my soil is combined with Canna Coco Professional Pro Soil, Sure Vermiculite, and Coco Peat. It holds moisture for a long period of time.

I have recently given them 1/4 of the manufacturer's recommendation dosage from General Hydroponics Tripart nutrition + CalMag. This is the second nutrition feed since the start. The PH level of the recent feed was around 6.4 but I have recently changed my PH meter as I believe the previous PH meter was broken and I could have given plants an unknown PH balanced water. I water the plants around 1littre each.

I need help to stop this from happening in the future any suggestions or recommendations?

Thanks

[Rwise]

I dont use coco, but I read it needs to be prepped first, so did you prep the coco?
It reads like a PH fluctuation, which you think you may have had.

[Hellogrowers]

Yes i prepared the coco prior to use.