I can share my recipe for a sponge growth media, but it requires about $500 in odd minerals and chemicals. The next best thing is Evian spring water because it has most of the mineral components that the sponges need for growth, but doing water changes with Evian is going to add up real fast!
Interesting, so Evian is not only drinking water but it can also be sponge growth media , I thought it tasted funny