About 3 weeks ago I setup a new 20 gallon long tank for my 7 month old African Clawed Frog. I use Seachem Prime and tap water, no substrate and a Whisper EX20 filter. Needless to say... I am in need of decorations for this tank since I currently only have a rock in the corner for him to hide behind. I had an idea to build some kind of castle/structure out of legos for the tank. I figured I could just put some rocks encased in legos in the corners to weight it down so it won't float. Question - Are legos safe to put in an aquarium for an ACF or do they have some kind of chemicals that will be harmful?