adding bowl rocks?

Could you be more precise as to what "bowl" rocks actually are? I have never came across that term in 40 years of fish keeping! Maybe we use a different terminology here in the UK.

if they're the red lava rocks(which i believe are frequently called bowl rocks, although it's spelled differently but i don't remember how) then they can be used but generally it's not a good idea because some might be full of silica and phosphates that they will leach out into the tank and fuel some really nasty algae blooms.