i use an old plastic library card to clean the algae off the walls of my tank. i find a scourer takes longer and isnt as effective. give it a go - but theres an old saying... no point reinventing the wheel....
make sure u clean the walls of the tank before u gravel vac though, it can get a bit messy (esp. if u r like me and dont clean the walls of ur tank every week) and a fair bit of gunk will get sucked up in the vac.
I wouldn't keep a red tailed black shark in anything less than a 40gal as they like to be able to move, plus saying that they can tolerate a 15gal dosn't mean they are happy, and then you will get fish keepers thinking that you can keep them in less than a 15gal, when we are trying to get them into the tank size they deserve.