A few things stick out to me:

1) 15L pots are pretty big for new clones in coco. Plants grown in coco like smaller containers compared to soil.

2) ph is way off. Should be between 5.5 and 6.2 with coco, many prefer in the 5.8-6.2 range.

3) Are your nutrients coco-specific? I'd check out Canna's site: About Coco | CANNA UK and make sure you are following there instructions.

4) Check your nutrient amounts according to Canna's schedule. From the pics it looks over-fertilized, but it could be related to your ph problem or 'contamination'.

I'd put them maybe a little farther away from that 600w, if you have some other lights like fluoros or cfl's, that would be even better, just to nurse them back to health. And find out what 'contamination' it was. Pests? disease?
bigtopsfinn Reviewed by bigtopsfinn on . im a nexbie hi. i have 4 cuttings. i am using growells advise. when i got the cuttings a couple had white/yellow patches on them. as they are growing, which today is day 5 there are more yellow/white patches and dots on them. i am using a 600watt sodium light which i was told by almost evryone i asked that it was fine. i think i may have put the light to close to the cuttings. but now i have highed it. 150cm away from cuttings. i am using canna coco professional soil. the nutes i am using at the moment Rating: 5