If you want to maintain a 30-50 ppm borate level I would suggest you read the thread "The Great Tetraborate Experiment" in the china shop first.

Second, the borax calculator in Bleachcalc has an error and underdoses on borates big time!

To incease your borates use this formula:
For every 1000 gallons 12 oz of 20 mule team wil increase the borate level 10 ppm and will need 6 oz of muriatic acid to neutalize the pH rise

SO

for your 25k pool to increase it about 40 ppm (since you are starting out at 8 ppm) you need to add 1200 oz which is 75 lbs which is approx 15 3/4 boxes of 20 mule team borax. You will also need 600 oz of muriatic acid or about 4 2/3 gallons to neutralize the pH rise.

Put in about 2 gallons of acid then about half the borax. Brush until dissolved. Put in two more gallons of acid and the rest of the borax and brush. Run your pump for 45 hours, test pH and add acid to adjust to 7.6 (You will need approx 2/3 gallon more, I would add about 1/4 gallon, wait about 30 minutes, test pH then add it by the quart, wait 30 minutes and test pH until you reach 7.6)

I can think of two reasons why your borate levels might be lower than the last time you tested them. First, do you have a sand or DE filter that you backwash? If you do that would be why your levels are lower, they were lost to backwashing.
Second reason is testing error, the borate titration test is one that is prone to slight errors and if they are using strips and a reader that is even more inaccurate. Good news is borate levels don't have to be very precise, just in the ballpark so raising your borates about 40 ppm should work out fine! When they drop to below 30 ppm it's time to bring them back up to about 50 ppm.

Hope this helps.