Simple question! What size glass diffuser would I need for a 40g tank? I'm planning to put it underneath the outlet from the Juwel filter to distribute the bubbles. I'm looking at either a Rhinox 3000 or 5000; or a Dazs Spiro. If the Sprio's up to the job I might try one of those as I will be able to see the bubble rate in the coiled section, right? As the CO2 pipe is going to be tucked down the back of the tank my conventional bubble counter will be stuck in the cabinet and I thought a way of quickly checking in the tank would be handy too - I understand the coil doesn't really help with diffusion, right?