I have two and they are fantastic algae eaters. I noticed mine appeared to have a liking for an amazon sword plant that was near her driftwood. I simply moved the plant away and no more problems.

They really should have some wood in their tank. I have two pieces and each bristlenose has established their territory based on piece of of wood.

The only other suggestion I have is perhaps they need more algae/green vegetable in their diet, perhaps increase the algae wafers, some boil zucchini.

Fred