You are getting algae because you are not keeping your chlorine high enough. Chlorine levels are dependent on CYA levels. With a CYA of 80, you should be keeping your chlorine between 5-10ppm ALL the time. Dip below 5ppm and you give algae a chance to start. Your shock level would be 20ppm.
So, test and add enough bleach to get back to shock level and try and keep it there until you meet 3 criteria:
1) You don't lose more than 1ppm from sundown one evening to within an hour of sunrise the next morning
2) You have no higher than 0.5ppm of CC
3) You water is clear and you have no algae spots.
Then, we typically advise keeping the chlorine high for one additional day and then let it drift down and keep it between 5-10ppm.
You will want to brush the pool while the chlorine is high and run your pump 24/7 while you are working to clear this up.
More about the CYA/Chlorine connection can be found here:> http://pool9.net/cl-cya/
Your K2005 kit cannot test chlorine levels past 5ppm. In fact, it will bleach out at high levels at make it appear that you have no chlorine. If you will pick up the K1515 add-on kit, it will give you the one test that the K2005 is missing that will allow you to test high chlorine levels. You can get it through this link:> http://pool9.net/tk/
By the way --- your pH readings will be invalid anytime your chlorine is over 10ppm with a Taylor kit (above 5ppm for other kits). So, if you need to test pH when the chlorine is high, mix one part pool water with one part distilled water and then test pH as normal with this mix.
Hope this helps.
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EDIT -- in a 25K gallon pool, each of the 121-oz jugs of 8.25% bleach will add about 3ppm of chlorine. Use that as a reference to help you figure out how much bleach you need to add whenever you test.
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