When people report having 40k gallon pools, more often than not, they have gotten an erroneous value for their pool volume.

Let's assume a 30K gallon pool: each gallon of PLAIN 8% bleach from Walmart will add about 3 ppm of chlorine to that pool. Effective algae doses, on stabilized outdoor pools, start around 10 ppm of chlorine, or 3.5 gallons

So . . . go to Walmart, and get a cheap OTO /phenol red kit, and 12 gallons of bleach. (If they have an HTH 6-way test kit, get that, too). Go home and add 4 gallons in the PM. Wait 1 hour (with pump ON), and then test with OTO. If the result is not DARK yellow, add another 4 gallons.

Meanwhile, if you got the HTH kit, test your CYA (stabilizer) level. (Read the instructions carefully -- you can only do the test 1 or 2 times.) As this page:
http://pool9.net/cl-cya/
correct chlorine levels are determined by your CYA level.

You're gonna the need the K2006 (both the HTH 6-way and the K2006 are made by Taylor), so go ahead and order one: http://pool9.net/test/

Most people find the kit somewhat intimidating, at first, but watching these videos will help: http://pool9.net/tk-guide/