Well I buy my water in gallon jugs or 3.5 liters of water. It's baby nursery water. It has a constant ph level of 6.5 . I try not to mix up more than a gallon at a time. That way it gets used up the next day when I feed. Also when I feed my plants, I use a garden watering pale. If I have 3 plants, and there all on the same regiment, then I just fill up the watering can (it's a small one) and pour one in each one and start back at the beginning and do it all over again until all pots have had the same amounts and there water saucer's are 1/2 full. Done.
Glad to help man.