I have the same issue with my 1000 gallon. I decided to buy two heavy duty magnets and make it. Or pay $900-$1200 for one. For now I have two Flag tails cleaning the algae.

DIYMAG Neodymium Fishing Magnets, 1500lbs (680KG) Pulling Force Rare Earth Magnet with Countersunk Hole Eyebolt Diameter 4.72Inch (120mm) for Retrieving in River an Magnetic Fishing
https://a.co/d/f8JeoAo