how to clean up an old tank

[Beverly]

Yes, I DO remember Jack. That was so long ago! He WAS a grumpy old guy.

A 5% bleach solution would disinfect the tank. Rinse really, really well, then use generous amounts of Prime in the last rinse water to neutralize the remaining bleach.

Bleach won't clean up the tank, though. As already noted, vinegar, a razor blade and elbow grease will work wonders

[gobytron]

Fill with water, add vinegear; 10-20% of total water volume should do.
add power head.

run for a day or two or three

From here, most algae with be gone and whats left will come off very easily with a razor.