questions about doctoring plant feed

I went out today in search of 15-30-30 for my newly flowering plants..I found 15-30-15 which is close enough, but I'd like to find a way to add something to the water to raise the potash a bit.

Also, I went in search of calmag today and I wasn't sure what to get. I've never been big on micronutrients so it's a whole new world to me this year. The only thing I found was calcium/magnesium/zinc supplements intended for human consumption. I'm not sure if that would work properly, because the calcium, magnesium, and zinc is water soluble, but I don't think the other minerals in it are water soluble. If anyone could tell me if it would still work, I'd appreciate it!

Sorry for the newbie questions ^.^!

Due to the large number of views and no responses, i assume either this was too long or no one knows.

For those curious, I did some more research and figured out that wood ash is a good source of potassium, but I think that has to be put in the soil, and personally i'm looking to add things to my water mixture.