I have a 1.5 gallon tank with a male Betta Splendens in it. Last night I cleaned the tank and took some gravel out, reducing the gravel layer from 2" to 1" thick. There is a 1" layer of top soil under the gravel. I have an Amazon Sword and Java Fern growing in one corner. This morning i noticed a grey "fog" seeping up around the Java and Sword from underneath the gravel. This was in an area where the gravel layer was thickest. Am i seeing gas or some sort of bacterial bloom? My Betta, Jareth is acting the same as he always is, he even swam through the "fog" and seems to be ok. When he swam through it it didn't stir up, just sort of shifted out of his way and then settled back.