You can make tanks work, but they certainly aren't intuitive the way other enclosures are. Just like you can fix a lot of things with duct tape and have it "work", yeah it gets the job done, but it's going to be a never ending fight of tweaks and modifications, and more fixes.
If you can post pics of your set up, we can troubleshoot better. Written descriptions always seem to miss things; for instance I can't see where you say if you are regulating your heat source. Remember that only the warm side of your BP's enclosure should be upper 88s to low 90s. Ambient should be 78 - 80. Heat mat needs to be regulated by a t-stat or else it can get over 120 and burn your snake. I would ditch the light bulbs and go with a single ceramic heat emitter.
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