singerteacher, it is possible to learn what a FC level of 6 looks like on a standard OTO test without dilution by comparing what you see to a FAS-DPD test a number of times. But it won't look like any of the color blocks on the color comparison chart that comes with the OTO test and many people have trouble telling the shades of yellow apart even with practice. The different yellows are distinct, but without a color reference it is tricky to figure out.
I really think that you can figure out a standard amount of chlorine to add each day, by experimenting for several days with the FAS-DPD test, and then use that amount for several days before rechecking how things are going with the FAS-DPD test. On the days you are not using the FAS-DPD test, a quick OTO test is good enough to tell you if things have gone significantly wrong, even if you can't distinguish the shades of yellow. If the OTO test looks off in any way then you can confirm with the FAS-DPD test.
If you are worried about being sure to keep FC at 6 or above, you can simple aim for a slightly higher level than that when figuring out your daily chlorine addition. With a little extra attention when there is a swim party or major storm, it really is possible to have consistent FC levels even without daily testing. FAS-DPD testing is important at least once a week so you can adjust things as the seasons change.
I really think that you can figure out a standard amount of chlorine to add each day, by experimenting for several days with the FAS-DPD test, and then use that amount for several days before rechecking how things are going with the FAS-DPD test. On the days you are not using the FAS-DPD test, a quick OTO test is good enough to tell you if things have gone significantly wrong, even if you can't distinguish the shades of yellow. If the OTO test looks off in any way then you can confirm with the FAS-DPD test.
If you are worried about being sure to keep FC at 6 or above, you can simple aim for a slightly higher level than that when figuring out your daily chlorine addition. With a little extra attention when there is a swim party or major storm, it really is possible to have consistent FC levels even without daily testing. FAS-DPD testing is important at least once a week so you can adjust things as the seasons change.