Not sure if my logic is correct,
Glass cleaner scrapes the 5 grams of algae, 5 grams of algae goes to filter.
Pleco eats 5 grams of algae, something like 3 grams is converted to energy, 1 gram for growth, 1 gram goes to filter as poop.
No. Polyurethane is not safe for your pleco. Would you drink a glass of it?
My 3D background is from Universal Rocks but I think this guy is sold on what he already has.A website I go to for a lot of tank decorating is called universalrocks.com. They have some awesome very realistic driftwood modeled after actual cypress and various woods.They are a little pricey is the hang up but they wont put any tannins or bacteria in the water if that is your concern and can clean simply by hosing it off. MY plecos love it. Anyways just a suggestion for you.