I've actually wondered about this myself. I cannot see standing water supporting the growth of microbes or competitor fungi any more or less than wet perlite. All I can see the perlite doing is increasing the wet surface area and therefore the evaporation rate but in a contained smaller space this shouldn't make that much difference.
Personally I hate perlite though so I may be engaging in confirmation bias. Don't like how it feels or how it scratches up containers.
Do be cautious of keeping the water level higher than the heater. They're very prone to overheating, cracking, and or melting if exposed to air while running.
Edited by 425nm, 23 December 2018 - 05:33 PM.