Tough Algae even with high chlorine

[PoolDoc]

Kit options:

HTH 6-Way Test Kit @ Walmart (OTO chlorine test)
Taylor K2006A (3/4 oz bottles) @ Amazon
Taylor K2006C (2 oz bottles) @ Amazon
Taylor K-1515 FAS-DPD @ Amazon -- complete K-2005 kit.

[BigDave]

I agree with Aylad - you need the K-1515 FAS-DPD. As soon as you use it, you'll know why.

For now, while you wait for the K-1515, to get your shock process going, you can use the dilution method to read FC and TC. You'll need distilled water, the Taylor instructions say tap but that will foul your test.

You appear to have a rebranded Taylor K-2005, if it's recent, the chlorine comparator tube is marked on the side - 1.8ml, 4.5ml, and 9ml. You usually fill to the 9ml mark when testing. Fill the chlorine comparator tube to the 1.8ml mark with pool water then add distilled to the 9ml mark. Test this diluted sample for FC and TC and multiply the results by 5. If you don't have the graduated comparator, you can do the same by mixing 1 measure pool water with 4 equal measures distilled water, test and multiply by 5 (this is the CarlD shot-glass method). Dilution testing loses accuracy but will get you started, you still need the K-1515 FAS-DPD.

Please test and report pH, TA, and Calcium Hardness as well. If your CH is relatively low, you can use calcium hypochlorite to reach and maintain shock level but if it's high, you have to use bleach / liquid chlorine.

Follow aylad's instructions for shocking your pool - it will clear.