Below is a link to a filter the same as I use, very basic/simple, sponge and a pump;
https://www.ebay.co.uk/itm/384939056024?hash=item59a027db98:g:ZEQAAOSwUmhieHTi
The ones I use have a seperate cap on the base, I remove that so there is more open area of sponge, and to remove the sponge for cleaning I just turn the whole unit 90 degrees on the glass and can then pull the sponge out, literally takes a few seconds and no dismantling/seperating of any of the unit. I use 2 of these in each of the bigger tanks.
I don't use anything other than the sponge or CO2 or Fertilizer in any tank!
I know how you feel about losing a whole tank full of shrimps, that happened to me when a heater stuck on and cooked them............... My second attempted didn't work and so the rasbora are in that tank for now. My first time with the taiwan bee shrimp was a terrific success and that was started with a small 3 gallon tank and then moved to a bigger tank (?), maybe that is partly the secret to success?
I like your fountain idea, it sounds very interesting. Did that incorporate some form of filter?