Hi Scolly,the siz of the containers is not really important,ive used several different sizes they all work fine.There again the filter just needs to be of the size to match the amount of water you have.If any thing over kill on the size.I clean the filter often so i only have a sponge and charcoal in it.Now the flow rate is important.I like a steady stream of water coming out of the tubes.It can be adgusted by the amount of air.The other thing that is important to keeping the flow steady and constant is maintaining the water level.When i get it just right i put a mark on the tub and keep it there.As far as water changes go i siphon anything thats on the bottom and then replace that much water,its usually not much. Hope this helps.If you need more,dont hesitate to ask,im glad to try and help. Tuck