Spots on Leaves

What could be the cause of this to the leaves in the picture?

Growing in coco coir with tap water (200ppm) pH 5.9, Canna Coco A + B (final EC 1.3)

Looks like a little CalMag is in order. Definitely seeing some low Mg going on there.

Epsom Salts will take care of low Mg and that's all it may be.

if your growing in Coco you need calmag as additive, must have. Some plants I find show it sooner then others, and also make sure to give full strength even on smaller plants of it, as the medium is missing it all together. I made the mistake of using it at half dose, three of 4 show no signs, one just started today. I upped to full and did a folier spray as well to mitigate it faster.
Your picture is exactly what mine looks like with the spots.....

Ok I'll start giving them some of this CalMag that I've got, thanks.

I've adjusted as you suggested and all of my plants look good except for one, whose leaves look like the picture below. Any idea what it might be? Once again they are being fed tap water (200ppm) with pH 5.9 canna coco a + b, GH rapid start (1.3 EC) and full dose calmag (to EC 1.9), temps 80-85F, RH about 55-60%.

Thats a new leaf?
The damaged will not recover and any young leafs with this showing at all will only look worse as they grow. You should see improvement in new growth so it may take a bit.
Your temps are a little high you should shoot for 78-80f other wise everything sounds good just give it some time to recover and grow some new leafs.

AlbertPremo said:

Thats a new leaf?
The damaged will not recover and any young leafs with this showing at all will only look worse as they grow. You should see improvement in new growth so it may take a bit.
Your temps are a little high you should shoot for 78-80f other wise everything sounds good just give it some time to recover and grow some new leafs.

Click to expand...

These are new leaves yes, this plant had no problems before.

Then I would go straight water Ph to 5.8 with Calmag (no nutes) and flush it real good.
Try got get your temps 82f max and make sure your light is at least 2 feet away.

the looks of it if new, seems like a PH issue, if its over 6.0 in coco its locking out the calmag, i know you say 5.9 but I would double check your PH readings as well to be sure before flushing.