I too bought the HTH 6 way earlier this spring when I opened my pool to a swamp with inch think green algae on the sides and bottom.
It is not sufficient for what you need to test. So you need a real test kit to get the FAS-DPD test for FC.
However, it does have one very useful test....CYA. My guess is that you use tablets for chlorine? Which probably means your CYA is off the charts high. Do the CYA test and tells us what it is at. High CYA reduces the effectiveness of chlorine, which means you need a lot more the higher CYA is. Also, likely you've added a lot of copper with the algaecide.
Please post your CYA test result because you may need to drain some water and refill.