I was looking for a spare CO2 diffuser and ended up chancing my arm on eBay by buying 2 from a seller in Hong Kong, one to use and one spare for when the other needs cleaned. listing The listing says that they are suitable for tanks of 55gals (don't know whether this is imperial or US, but as my tank is only 185litres the diffusers are overrated either way). However, I received them today and they're about half the size of my current diffuser, a Dymax 105 which was rated about right for my size tank (I think). So if these ones are half the size, will they do the job individually and how will I know if they don't - I presume I just measure CO2 and if I can't get a decent reading, they're not doing the job *shrugs*? Cheers in advance!