Back in the tank today to work out how much extra weight I need to achieve neutral buoyancy. I bought a few 1 pound scuba weights so I could quickly approximate what's needed. Popping the ROV in the tub and then putting these on it, I found I need between 3 lbs (it just floats) and 4 lbs (it just sinks) to achieve neutral buoyancy. I'll buy some finer, more permanent, weights so I can dial it in and zip tie them to the frame.