Happy days mate, at least you have a new happy home for the fish as they get bigger if needed.
The auto water change units are great. Make everything so easy. you do lose a bit of new water but lets be honest the trade off is well worth while. an example and my opinions below:
510 Litre tank. you would buy the 57 Litre auto water change unit.
Mix 57 Litres of fresh water in the unit and connect it to your tank + turn on.
You will now have a system with 567 Litres. 57 Litres of new water. 510 Litres of old.
Once this has all been mixed you remove the 57litres of water.
The easy maths looks like this:
567Litres = 57 Litres new water, 510 Litres old water
taking 57 litres from a 567 litres system is taking away 10.05291% (57/567*100) so lets call it 10%
This means you have lost 10% of the fresh water and 10% of the old water. meaning by doing a 57 litre water change results in 5.7 litres of new water being thrown away and 51Litres of old water disposed of. (in case someone wants to be exact its actually 5.7301587 litres of new water lost and 51.2698413)
My opinion the disadvantages the obvious loss in the new water.
the advantages. No shock to the system during the water change as everything mixes and changes slowly. Water levels stay the same allowing all equipment to stay on. Its a million times easier. no syphoning to a bucket / pumping water out. they make life a lot easier. easy to do more likely to happen !!
if i had more cash i would definitely get one. Look a top bit of kit.@reefloat
can you confirm what i have put above is right ?