new - free chlorine levels constant at zero

Hi I am new here.
We have a 12000 gal plaster pool in ground that sits in the sun all day.
My o rings for my DE filter backwash went bad so a lot of my water was being pumped into the sewer, it introduced air into my filter so it didn't filter properly for 4 days (this is my first pool I had to wait for a pool guy).

After we fixed that I am having a hard time getting rid of the greenish water. I got these test results from the pool store about my water:

Free chlorine 0
Total chlorine 0.6
Combined chlorine 0.6
phosphate 300ppb (recommended 0-100) - no idea what to do about this
pH 8.0 (I added muriatic acid)

here is from my test strips
pH ~ 7.5
hardness ~ 200
free chlorine 0
cya ~ 40


anyway, I shocked my pool with chlorine shock and it got most of the green away, but it's still not clear. The paperwork they gave me suggested to use a superchlorinator (shock) and told me to use 1 lb of . I also have one of those chlorine tablets floating, but every single day I get a reading of 0 free chlorine and thus the algae is not dying. Should I shock again? It's been almost a week. I'm not sure what to do here. Let me know if I forgot any important info

You can just use plain bleach. Many of us use Walmart's generic 8.25% bleach as our source of chlorine. We don't trust pool store testing too much and we trust test strips even less. But..... for now, since we have nothing else to base advice on, I'll assume your CYA is 40 until we know better.

How high you need to shock a pool to kill algae depends on how high your CYA level is. Take a look at the chart at this link that shows the connection between the two. http://pool9.net/cl-cya/

So, with a CYA of 40, you need to shock your pool up to 15 to kill the algae. I have no idea what the ingredients are in the products you have so I think it is safer to just use bleach at this point. In a 12K gallon pool, each of the 121-oz bottles of 8.25% bleach will add about 6.5ppm of chlorine. So, go ahead and add about 2.5 of those jugs. Keep the pump running 24/7.

You need to get a good drops-based test kit. The test kit that we think is by far the best is the Taylor K2006 or 2006C (better buy). Not available locally but you can get it through this link that takes you to Amazon: http://pool9.net/tk/

But, in the meantime, go to Walmart and see if they have the HTH 6-Way drops-based kit (no test strips!) and get that. If they don't, get an OTO/Phenol Red kit (yellow and red drops) instead. Use it to test and then post your numbers. Also while you are at WallyWorld, get several jugs of their generic 8.25% bleach, a couple of boxes of 20 Mule Team Borax (laundry aisle) and a gallon of distilled water.

An OTO kit can only read chlorine levels up to 5ppm so you'll have to just judge the reading based on the color since I am asking you to take it higher. Use this chart:> http://pool9.net/oto-chart/
(The K2006 kit can read chlorine levels WAY higher than 5.)

Each day, you'll want to test the water and add some more bleach. You'll want to keep your chlorine in the dark yellow range on the OTO kit until you can go from evening to the next morning without a huge drop in chlorine.

Hope this helps a little. Repost if you have further questions or to keep us up to date on how things are going.

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