fifty gallons can be drained into a brute can, rendering the entire system accessible that really changes the game. Figured it was 150 gal
That being said, there's still the willingness to access factor and that removes just about every reef tank owner

they demand zero access work, they'll sooner take the tank down w loss $ than use access to cure the concurrent conditions. They'll refuse to touch it, rather watch it disintegrate its fascinating behavior we log this in work threads commonly
consider saving accessibility restoration for the very last step no need to downsize further. Right before total takedown when everything possible has been dosed, try our cleaning method. It requires totally cleaning your system and detailing rocks back to good condition directly, outside the tank. Dosing no more chems, gfo offline, new water, and a different way of handling algae on round two. Message if you want I’ll show you a work thread with more than one tank restored
That you have no sand really helps big time in cleaning approach
Post full tank shot
We could do to your reef what a dentist does to a bad mouth, several similar actions actually.