Fish entering and exiting the caves will naturally move water in and out. You should be fine. :thumb: :fish:

Keeper

 

Water, much like air, diffuses, so the quality of the water (chemically speaking) should not be significantly worse than the rest of the tank. The biggest problem is the accumulation of decaying material being trapped. Fish will disturb this, as will running your hand over it, or siphoning it directly during cleaning.

 

I use a small powerhead in my hand to blow out each dead end cave when I am doing a water change. Seems to work really well.