Another PH/KH/Co2 ppm Profile question

[Solex]

LED lights are on for 9 hours at maximum 40% of their capacity.
KH color test (with a Sera drop set), color change at the 7th and sometimes 6th drop, tap water is at the 8th.
Water temperature 22.5-23C.

These drop tests are not very accurate!!

PH (Sera drop test set)
08:00 >7 14-21 ppm (KH7, lights off, Co2 off)
09:00 >7
10:00 >7 (Co2 on)
10:20 <7
11:00 <7
11:30 6.5 66 ppm
12:30 6.5
13:00 6.5 (KH6, lights on 0-40% in 30 minutes)
13:30 >6 (lights at 40%)
14:15 >6
15:30 6 132-210 ppm
16:30 6
17:00 <6 off the scale ppm
20:00 <6
20:30 >5.5 (tinting towards yellow, fish and shrimps are doing fine)
21:00 >5.5 (KH7, Co2 off)
21:30 >5.5 (lights 40-0% in 30 minutes)
22:00 Lights 0%

Looking at the table, I am pumping in excess Co2.
http://www.barrreport.com/showthread.php/12022-CO2-pH-KH-table

Were do I start? Getting the 1 drop of PH at the moment of lights on or the ppm level at 30-40 ppm at lights on?

 

[Martin in Holland]

If plants (and fish) are doing fine you could start injecting CO2 a bit earlier and stop earlier too...tinker with it until you get a more stable CO2 level during the whole lights on period.

 

[Edvet]

Using tables to gauge CO2 levels is too inaccurate, many more things have influence on pH, droptest are too inaccurate to do a solid pH profile.\
Try to borrow a pH pen/test for a day.