Last year I used a new type of Perlite(it has no chemicals) its really alot bigger chunks of Perlite so the light diffuser will not sink at all. I had a 13 egg clutch and it didn't even begin to sink not once, worked like a charm. My buddy told me about it as he sells plants(bromeliads) at all the plant shows. I forgot the name of it but I'll call him later and get it..