It could also be that your water has a high level of dissolved minerals in it (hard water).
Or, it could also be that the fish you have could be the type that make bubble nests to mate. What type fish?
If you're able to test your water and post the results here it would help give you a better idea of whats happening.
If it's being caused by the water condition, a water test will tell.
ammonia?
nitr
ite?
nitr
ate?
GH?
KH?
Ph?
