Water storage and water changes.

I’m pretty sure I haven’t been doing my water changes properly and thankfully I have hardy live stock at this moment. Been storing my water in sealed jugs under my tank which I’m sure helps keep it warm but not as warm as the tank. Then mix the salt a hour or so before I add it to the tank. Read some archives on here and people have there salt water premixed in the brute can with heaters and water pumps is this the correct way of doing this? Maybe not correct as there hundreds of ways of doing the same thing but the better way for our live stock? Is there any issue with algae or mold growing ?