firstly try alarger water change remove as much as you can when taking water out of your tank vacume your sand you will be amased at how much chap is in it. your cousin may have been over feeding, what I do is use a auto feeder that way that way I know how much they are getting. also clean as much off your rock as you can. What you can do is take 1 piece out and scrub it and using boiling water slowly poor it over the bad area but not the whole rock this will kill the root but keep most of the rock alive. Do not do this to all your rock at one time just one piece every day or 2. and do lots of water changes and vacume the gravel every time. get a sand sifting star they work wonders as long as they have food. I nolonger have to vacume most of my gravel. I do the areas the sand star does not like to go.

Bill