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How much UVB is filtered out by water? The way my tank is set up, ,I can't have the UVB over the basking area, so I put the turts fav. plant close to the surface of the water, and have the UVB above that. He's usually between 0-2 inches in the water, under his uvb.

Question is-- is he getting enough UVB, or do I have to rig it over the basking area

I think it was somewhere over 80-90+%. Considering most lamps can only produce 3-10%, its almost pointless unless it's over the basking area.

UVB rays penetrate water to a certain extent, and it depends on how deep in the water a turtle is swimming. The sun is much, much stronger than any UVB light, and I think I remember reading that its rays penetrate the upper few inches of water (loosing strength with depth). But most UVB lights give off so little UVB rays in comparison to the sun that ideally they should be as close to a basking turtle as possible (this is are regular UVB lights, not the MVBs).

I remembered studing about that in Science this year, but I don't remember what the % was.