You've got to be careful about cleaning the tank because of the water. Have you been doing partial water changes? This will usually help to keep the tank fairly clean.
I'm trying to rack my brains but I think they suggest if you need to clean the tank, you should transfer the fish WITH their current water, into another bowl or something. Clean the tank and replace the fish, again with their old water, back into the tank.
I can't remember whether cleaning the gravel was recommended or not.
You should find lots of good tips on the web (I can't post links ).
my mum has an orb, and tbh it is the bane of her life at the moment. It is so complicated to clean out and get the right chemical balance. It needs cleaning every 4-6 weeks, but when you clean it, it goes really murky for a good week or 2 until it sorts itself out. Try google or the pet shop, you really need to get it spot on otherwise the fish will be floating.
Do you mean how much the bioorb tanks differ Sullysmum? I think that clip Lewis posted applies to all tanks. I have a normal tank and think the same principles would apply. Am going to get the gravel cleaner out some time today and be brave