Hey northman, I will attempt an answer, but keep in mind I am still learning too
I had a lot of those questions when I setup my first planted tank (a used 55g btw)
I would scrutinize this
thread for details, but I can tell you I am running 2x54w t5ho over a 55g and it is high lighting. It is suspended about 8" above the top of tank and an 8hr photoperiod.
When I started, I set the light right on top of the tank and ran it for 12 hrs a day, within a week the whole tank was covered in algae. Of course, at that time I was using 6x2L diy co2, which I am sure didn't help.
It seems to me that the moral of the story is: the more light, the better and faster growth if
you balance co2 and nutrients to match that light level.
Well that's easy to say, actually doing it though, I find challenging.
It's much easier to simply reduce the lighting, by raising it or window screen etc., thereby reducing the demand for co2 and nutrients.
In my 55g, I have 40 cardinals and 4 otos atm, and they are what I used to gauge my co2. I too built a clumsy drop checker that changed colors, but at the end of day who cares what color the drop checker is? What you care about are a.)the plants getting enough co2 and b.) can the fish be comfortable with the co2 level
I'm not saying dc's can't be useful, but you will likely end up with less co2 than is possible, if you rely on that only.
I slowly increased my bps until the cards all hung out at the top, then I backed it off until they were fine and this is where it has stayed. If I put a drop checker in there it will turn yellow.......does this matter to me? not at all
Don't gas your fish, just patiently adjust and observe with the goal of maximum co2 and healthy fish in mind
I also use a diy reactor, do ensure there is adequate flow to deliver the co2 and nutrients around the tank. I like hydor koralia, or circulation pumps as opposed to powerheads, an opinion
Finally, I would add that you should avoid allowing nitrates and phosphates to fall to zero. When you give plants high lighting and high co2, the demand for nutrients also rises in a corresponding way, therefore if there are no available nutrients the plant will suffer
Anyway, some rambling thoughts to consider, best of luck to you