I have recently bought a flexible air curtain (bubble wall) and an air pump with a check valve. I put it in the tank after a rinse and I don't know how to keep it straight as it is flexible and always to twist and curve.
More than 10 years
You could try placing some heavier rocks or some type of ornament on each end to hold it down and prevent it from curling.
Maybe placing it deeper into the substrate would be another option.