i'd do as jondamon said above mate with the exception of adding the chem ferts i'd ad a little piss to the water so as to make sure there's nutes there, also i think your gonna cause probs mixing up 1 litre at a time mate ph down seems to be a funny thing and the less you can get away with adding the better. a cheap alternative would be a standard bucket 3gal you can usually pick them up for a pound or 2 when i was buying them to turn into pots i was paying a pound each for them in bnq and asda also plastic storage boxes can be picked up for a couple of quid but i don't know how much liquid they hold so without working it out measuring your nutes will be tricky