In the Tropical it's just a blue airstone + Rena 100 pump (the airstone is under the gravel beneath the rock arch)
In the coldwater there's a 24" air wall and a ceramic airstone + Rena 200 pump(the airstone is inside the fake log)
The ceramic airstone is more expensive but lasts longer and produces lots of fine bubbles, the blue airstone is just cheap
The coldwater is going to have 2 black moors & 1 ranchu in it and they love to play in the bubbles which is why i've gone overboard in that tank
The only reason i got it was that was the only 'reasonable' colour the LFS had when i set the tank up. The rocks are green savvana stone which does look nice with the green gravel (but does show in the pictures very well).
I will be changing the gravel to either natural colours or sand, not sure which yet. It means changing the rock as well to natural river stone or slate.
It all depends on whether i can transfer the green stone to my girlfriends coldwater 30g (it cost too much to throw away) as that is for her goldfish and the she wants pink gravel