One approach is to monitor CPUE. Has the CPUE (catch per unit effort = time needed to catch the same # of fish) gone down? If so how much ? The numbers of fish ( 10 lbs to 50 lbs) per acre depends on the ponds fertility/productivity. If it starts getting more difficult to catch lots of 10-12 inch LMB then cut back on removing them like you have.

Another approach is to watch for improvement in Wr (relative weight). Have you been keeping that type of info?

A third method is to do a seine survey as per Swingle to see if you have lots of 3 in BG, along with yoy BG and LMB. If those #s are right it means you are approaching balance.

All 3 plus visual and creel info should be enough to give a solid answer. Based on your comments I think you may be closer than you think to balance.

In a very clear pond like you described you may only have 25-30 lbs of LMB per acre. If so you can't take out more than that. In a very fertile pond you could have 125 Lbs of LMB per acre. So it depends. No clear cut rule of LMB lbs per acre can be given without lots of good data.