My tank is 75gal low light, medium stocked community freshwater with at
least 1/3 plant cover, no CO2. For the past couple of weeks I've been
adding Flourish, Trace and Nitrogen at the recommended rates, and do a 50%
water change weekly. The plants have improved in colour and growth very
noticeably.

Tank water: pH 7.8, GH 6, KH 5, Nitrate 5, Phosphate 0.75 (Tap water is
8.4, 3, 3, 0.25)

I've finally begun to try to raise the KH in an attempt at increasing the
CO2 level, so added 3 tsp baking soda, which produced little change, then
added the recommended additonal 3 tsp today, which brought the KH up to 8
and didn't affect the pH. So far so good.

Looking at the standard CO2/KH/pH table, it seems I need to increase the KH
to about 20 to even get close to the optimal CO2 level. Which means I'm
going to be adding a lot of baking soda each week. My plan is to add 6 tsp
daily, monitor KH & pH, until I get up toward a KH of 20, and then, once I
know how much to add, add the appropriate amount with my weekly water change
in order to maintain the high KH. Does this sound like the right approach,
or am I about to create another disaster?