If the red 'stuff' blows off, it is cyano
and not a good thing. It indicated a nutrient issue int he water column. This can come from overfeeding as well as disturbing the sandbed, aka moving a tank from point a to point b. Brush and siphon it out during your weekly water change, make sure you use ro
at worst) for top off and water changes, and minimize feedings (2-3 times a week). It will take time, but it will eventually solve the issue.