I would buy one too if it existed. Water change only unfortunately.
How much is the RO water?
Another alternative is to collect rain water. Is you live in your own house, go get a small-ish rain water tank and connect it to your gutter down pipes. Not sure how much tanks are in your area. I can get a 100L raintank for about $50 and it is easy enough to diy install.
There is a small initial outlay but is free after that.
I use an American Filter jug by ZEROWATER to get RO water. This is obviously the easiest route for you as it is available everywhere in the USA (Walmart etc) and you just use tap water and will be much cheaper there as it is an American product, they have a USA website you can get details and buy from as well? I then mineralise the water with the usual shrimp products!
I hope this is of some help but I don't use canister filters so can't help you with the rest unfortunately!
I decided to get a canister filter and keep a fry screen on the intake. I have yet to set up.
I also set up simple PVC pipe water bridges. It was so simple. Thanks for the idea!
im hoping that the water displacement from the canister filter’s intake and output tubes (each in separate tank) will move water and temperature through the pipes by balancing the water levels.