I was told to just bend the clips a little to make them fit better. Which Ive done, but yeah they are just little metal clips with a thin piece of metal that slids thru them to clip down the lid to the canister, which btw you lose really easily as they drop off every time you move the canister 
The lid itself once the canister has been working is nigh on impossible to remove for maintenance as it literally vacuums itself on.
To be honest, I dont know why these are rated so highly, personally I think they are made from cheap materials and nothing like as solid as fluvals or tetratecs. Worst purchase Ive made so far in several years of keeping fish.
Oh and no airstone/diffuser on any of my tanks.
The lid itself once the canister has been working is nigh on impossible to remove for maintenance as it literally vacuums itself on.
To be honest, I dont know why these are rated so highly, personally I think they are made from cheap materials and nothing like as solid as fluvals or tetratecs. Worst purchase Ive made so far in several years of keeping fish.
Oh and no airstone/diffuser on any of my tanks.









