Thanks. I followed your directions and got an answer (about 6 lbs).

I am wondering if I have Mustard Algea. Do you know where I can see a photo of it? To get rid of it requires an algeacide containing copper, right? (Has anyone tried placing copper tubing in the pool instead?)

Here is some mustard algae:

Mustard algae tends to grow on the walls of the pool on the shaded side.

No, you do not need a copper based algaecide. Copper can be troublesome and is best avoided.

Thank you for the photo. Unfortunately, the algea depicted looks a lot like mine. What algeacide should I use?

I shocked last nigh with the does of calcium hypochlorite recommended by the Pool Calculator. These were my readings before: CYA 55, FCL .2, TCL 3.6. These are my readings this morning: FCL .4, TCL 6. Not much difference, right. Maybe I did not use enough shock? The Pool Calc says I need a shock value of 17 ppm (32ppm if I have Mustard Algea). What should I do now? Should I shock, wait an hour, and test the water, and add more shock, and repeat until I reach 17ppm (noting the total amount of shock I used)? Then repeat shocking according to the directions in the article on shocking?

Here is what I would do:

First shock to normal shock level, with CYA of 55 that is 17, until the mustard algae appears to be gone. Brush everywhere at least once a day and preferably more frequently. Then shock to 32 for two nights, taking special care to brush everything while the FC level is around 32. The first shock to around 17 is done according to the normal directions. The second period of extra high shock needs to be done in the evening so you get as many hours as possible of extra high chlorine levels before the sunlight starts lowering your FC level.

Chlorine kills algae, algaecide helps prevent it, not kill it.

I agree with Jason's advice above.

Follow the instructions in shocking your pool. Add chlorine according to the pool calc, test after 30 minutes to ensure you reached your shock level, adding more if necessary. Test again in the morning to see what your levels are, adding more to bump back up to shock. During the day, if you are home, it helps to test as often as every hour, adding more bleach if necessary to hold your shock, because of the sun it disappears quickly. The sooner and more frequently you can hold your shock level, the faster you will kill the algae. It's going to take a lot of bleach.

Be careful adding cal-hypo as it raises your CH level. What is that test result for you currently?

Remember, filter 24/7, brushing at least twice a day, shock until your water is clear and your FC holds overnight, or you lose less than 1ppm in the dark, and your CC's are less than .5

Also after this is complete run your pool with the "mustard-minimum" of FC for awhile to help prevent it from returning, don't let it go below that target. If this is a persistant issue with your pool, consider PolyQuat 60 algaecide but normal use of algaecide in a properly balanced and sanitized pool shouldn't be necessary, the chlorine at proper levels should do the trick.