I've had pothos in water like this and the water getting murky really isn't too much of an issue. The biggest problem I've seen is with dust settling on top of the water. Maybe consider making lids with cut outs for the different stems (sort of like a toothbrush holder)? You'd keep a lot of the dust out, help limit some of the evaporation so you have to fill it less, and be able to pose the stems much easier as they grow.