Help with Chlorine Loss

[PoolNoodle1]

Hi all. Im new to this forum and have had my pool for about a year and half. My problem is that the chlorine level keeps dropping rapidly. Last year everything was fine and I was adding only the dichlor 3" tabs. But this year the chlorine levels keep dropping too quick. Also it turned green a few of times due to these drops in chlorine. I had to shock it and the green went away. Just in the last few weeks, Ive put probably 10 gallons of liquid chlorine, about a dozen dichlor tabs, a dozen of the shock bags (Pool Time Shock Max Blue 6 in 1), 4 pounds of HTH Ultimate Mineral Brilliance, and also algaecides, clarifier, ph up, baking soda.
So 2 days ago I put two 1lb bags of Shock Max Blue, 2 gallons of liquid chlorine, 4 dichlor tabs, and today when I checked, the chlorine was almost 0 ppm. So today I put 1 more bag of Shock max blue, 1 gallon of liquid chlorine, 24 oz of ph up, and 10 oz of stabilizer (which I never did before since stabilizer comes mixed in with the granular shock max and 3" tabs anyway). I decided to do a water test about 15 min after I put the chemicals and these are the results at the moment.
Chlorine - above 15 ppm
Ph - 6.7 or 6.8
Total Alkalinity - 60 ppm
Total Hardness = 290 ppm
Cyanuric Acid = 70 ppm

I know that the chlorine will drop dramatically in the next day or so. If anyone can help me as to what is going on here. Could it be the heat? (It has been over 90 degrees and sunny for almost the whole month). But even with the heat, the chlorine levels shouldn't drop that quickly. Btw, I'm in Long Island NY area, if that helps. Pool size is 18000 gallons oval. Any help is appreciated. Thanks in advance.

 

[mknauss]

Welcome to the forum!
How are you testing your pool water chemistry?
You need to follow the SLAM Process
I suggest you read ABC's of Pool Water Chemistry.

 

[JJ_Tex]

One of the pillars of this site is maintaining your FC in accordance with your CYA. See my signature for the chart.

While your CYA is a bit high, it is still manageable (dont add any more stabilizer or tabs as they have CYA). Of course since you have algae, the first stem is to SLAM as mentioned above.

 

[PoolNoodle1]

Hi. Thanks for your replies. I have a few kits that I test with. If im in a rush then I use the strips but usually use the 6 way test kit made by hth i think. Its not the super expensive one. It was $45 I think. Im pretty sure the results are accurate because I tested with 2 kits and a test strip. They all gave about the same numbers.

How do I test Combined Chlorine to get to 0.5 or less?

 

[mknauss]

With the addition of a FAS-DPD test kit, your 6 way should work. I assume it has a CYA test.