1) what is the volume of the blue scoop?
2) how frequently do you water?
Ray, As you know I sell this.
The spoon is 1ml to two litres.
I've just run a test of three batches of Rain mix and all adequately dissolved and all in the range of 250-350 ppm, level ish spoons, not heaped. This as you will know could give big differences.
I've used it for 7 years and not had such issues so I'm baffled, I've even directly sprayed my 100 Neo collection, no adverse reactions at all.
I've just done a video which I'll upload tonight to Love of Orchids & Gardening on YouTube. I show all three batches, pour on to three separate plants and see if there's any reactions.
Akerne's also water their whole collection 10000+ plants and sales plants, I know they aren't selective and again no problems.
I think what they did establish was they don't advocate stock solutions as you can get dissipation thus the solution becomes insoluble. I noticed this with powdered feed before and noticed calcium would just sit there when I once tried K lite.
Saying this I've mixed stock solutions and never noticed any adverse reactions, I do have a couple of indoor Phals which I was solely mixing from a strong stock solution and these two plants do have brown stains on the surface roots, they also get pushed to the max and fully dry before I water.
The powder for Dani looked like it contained too much moisture hence she noticed white specks once mixed, (CaS04) which had become insoluble.
Another reason was plants do not receive enough water so some of them dry out as a consequence. The roots in the pots are in a moist environment and can transport whatever moisture there is available to the plant, the ones in open air do not succeed in this and dry out.
Think they also established a drop of water(10-50uL-microlitre) in size on a root tip would contain 5-25ugr of Rain Mix at 1/2g per litre, which is insufficient to cause any burns so that was ruled out.
I'm still loving the stuff and see no reason not to use it.
Like Akerne's I also like to give them a good soak, I cannot tell you the pleasure I get on a Summers evening pouring water over them with a can rose like it's raining.
So to conclude maybe the key is to soak your plants and provide humidity.
I also think this is relevant to powdered feeds not just Rain Mix, there is another YouTuber that doesn't use Rain mix but another brand and she also gets some brown staining to the surface roots.
It would be good to get your thoughts on this Ray as you know MSU, powdered feeds and chemistry like no other for me.
I know very little on that side and to be honest haven't any interest to know that deeply.
Regards
Keith