I'd rather use my Best Guess Chart, here;
http://www.poolsolutions.com/gd/best...ine-chart.html
not just because it's mine rather than TFP's, but because I don't like the 'fake' precision implied by the TFP version.

Even with the K2006, you cannot reliable distinguish 70 ppm CYA from 100 ppm!

As far as getting your CYA up, don't do it till
(1) your water temp is 70 or more &
(2) you have fully cleaned up your pool.

The reason the SWCG makers want higher CYA levels is they their units are too small to maintain chlorine levels at lower CYA levels -- which is a bit sneaky. However, I do NOT recommend using your SWCG to clean up your pool -- do that with bleach or what have you. Use your SWCG *only* for day-to-day clear water operation.

Since you can access to trichlor inexpensively, get a couple of floaters, and use trichlor. That will raise your CYA, by the time you open!

You can put trichlor tabs in the skimmer, but if you do so, you MUST leave your pump on 24/7 -- otherwise, the chlorine solution in the skimmer will get too concentrated, and can damage a variety of things.

BTW, if you have a friend who has a Sams or Costco membership, you should be able to get BOTH trichlor and dichlor there very inexpensively in their "PoolBrand" brand. And, it's plain dichlor or trichlor, with none of the goop the other companies are adding these days!

Oh, and buy some borax -- several boxes -- and use it to raise your pH a bit. With both dichlor and trichlor, your pH is going to tend to drop. With your pool, you can dump a box -- not too fast! -- into the skimmer, with the pump running. This will not only raise your pH, but will (over time) build up a borate levels that is algistatic.