I get what you’re saying, but I was curious to do some reading on what had changed while I was away.
It was co2 on and off, lights on and off with no adjustment, 40par at the substrate was highlight and t5 was the king when I joined this game, with ramping lights and probes and supernova power leds I figured things had moved forward more than me so it was time to catch up.
First post I have read that asked the question of variable light intensity during photo period and CO
2 injection to match. You are correct lights was mainly on or off and variable intensity T5 was costly and not many folk used them.
With intensity variable powerful LEDs the plants need for CO
2 will vary
On my 500L tank I had four Kessil 160s variable intensity and six T5 tubes constant. Which came on at various times so the CO
2 need of the tank varies over the photo period as the kessils ramped up and the T5 came on. The ramping down isn't so much of an issue as far as I am aware as as
@ceg4048 has posted after 4-5hours and plants have had their fill the [CO2] isn't so critical.
What I did to combat the varying intensity/need for CO
2 is use different CO
2 injection rates. Well when I say variable they injection rate was constant, however having fitted a
PLC (programmable logic controller) I am able to do many on/off during the Photo period with a bit of software programming, also made easy by
@ian_m brilliant 'TankyMyTank' software design to control/adjust all on/off times by just adjusting one time - Its a work of art by Ian
example
1. CO
2 on till lights on - CO
2 twin injection on ( one CO
2 injection was at a high rate and the other at a lower rate)- 1.0+ph drop in 30 mins
2. Lights on both CO
2 injection off for 5min to 10mins, then lower rate came on a cycle of say on 5mins off 1min for 30 mins whilst the Kessil ramped up then as the T5 came on the low rate CO2 injection would be on constant till CO2 off
With a PLC using a bit of software to have multiple on/offs is vary easy, for a normal timer it would be tricky to say the least.
Are variable CO2 injection rates needed - dunno, but if you can 'emulate' variable injection via advanced on/off times why not, as the a stable pH/[CO
2] is easier to achieve using them IMO.