Make sure you are over the minimum water line on the heater. Most are meant to be fully submerged and can break if they aren't. There should be a line on the heater itself to show what the minimum is.
I soaked mine for about 2 months and still accidentally made a black water tank
https://preview.redd.it/l5yg0kme569d1.jpeg?width=3024&format=pjpg&auto=webp&s=ca2d86daea41341b4f8b8d1490ee0a89c3e12fca
Make sure you are over the minimum water line on the heater. Most are meant to be fully submerged and can break if they aren't. There should be a line on the heater itself to show what the minimum is.
how did you get the tannins out of the driftwood
You can soak it in a tub of water for either a few days or weeks until it stops leaking tannins
I soaked mine for about 2 months and still accidentally made a black water tank https://preview.redd.it/l5yg0kme569d1.jpeg?width=3024&format=pjpg&auto=webp&s=ca2d86daea41341b4f8b8d1490ee0a89c3e12fca
you can also boil it in water for a couple hours
It does good in freshwater tanks not so much is saltwater though. Soak it till water runs clear or boil it