I'll have to try the rock test now! great info! I added a background to the back of 5 gal it's not catching any outdoor light but this all started after the ludwigia was dying I thought to add 10drops of seachem flourish and after few days algae started covering everything. tested out dechlorinated filtered water which seemed to work ok with scrubbing. so that's how I've been keeping it at bay but it attaches to my anubias leaves rather quickly. I picked up 1 mystery snail and a few shrimp which seems to be doing wonders!