A question about fertilizer
 

I was wondering if things like seaweed fertilizer cal/mag supplements and normal fertilizer break down once they are mixed with water. I usually mix up a gallon at a time so I can be accurate with the amounts but I never need to use a whole gallon in a watering session. Is the left over still good to use or should I be mixing it fresh every time?

How many orchids do you have?

I have 18 orchids and I go through about two gallons of fertilizer on watering day. I mix my fertilizer at one quarter strength and then water my orchids with that.

I will let it sit for a week. If the color seems to have changed, or if it smells, or if I just don't trust it, I toss it and make fresh.

Not sure if this is the right way to be doing things, but it's worked for me so far. :D

First of all, even though the label usually tells you how much to mix in a gallon of water, you don't need to mix a gallon. You can mix a half gallon with half as much fertilizer as you use in a gallon. I sometimes use those cheap hand spray bottles from Home Depot that hold 1/4 of a gallon and I mix 1/4 as much fertilizer into it. Second, Fertilizer is just mineral salts so if you want to mix a gallon, you should be able to keep it without any problems other than maybe a little algae growing in it. The same is true of Cal/Mag. It should keep fine. I'm not sure about seaweed products. Since they contain plant enzymes and hormones I don't know how storing a mixed product would affect it.