How do you know the correct injection rate for Co2, is it possible to know before adding plants?

[John Troy]

Im currently dark cycling a 20L nano cube, I have a Twinstar 300E lighting fixture and I'm planning to inject CO2 and fertilise.
What I'm still confused about is how I'm supposed to ascertain the amount of CO2 to inject, obviously for optimum plant growth conditions I should be aiming for 30ppm, but how do I know if I'm injecting enough or too much.
Of course I can use a drop checker or instead the pH drop method, however if I use either of these two methods it will mean I need to constantly fluctuate my CO2 until I find the correct bubble rate for my specific system. Surely this fluctuation will cause algae? Is there not any way to accurately determine how much CO2 I should be adding in advance of introducing plants to prevent any initial melting/algae due to unstable conditions?
Also any method I can find online requires constant observation/testing, which is unreliable and time consuming, not to mention any difference in initial water parameters such as Kh, water agitation, flow etc can make this even more difficult. Watching a drop checker the entire day, or taking numerous tests doesn't to micromanage everything doesnt seem very reasonable.
So how do most people determine their specific injection rate, Is it just a case of trial and error, Given plants are constantly absorbing CO2 doesn't this make it more difficult to keep a constant 30ppm without changing the amount of CO2 injection throughout the day? Am I missing something or do I have a misunderstanding, thanks in advance.

 

[Scaperinc]

There are few in depth posts on here which you can read through.

Few things to have / consider you planning to have pressurised co2 system or diy?

1. Is your water soft or hard ?
If its hard you need to start injecting 2-3 hours before you lights come on. If it's soft 1-2 hours should be fine, co2 off 1 hour before lights go off.

2. A ph test or better digital ph meter.
Test your tank water before co2 starts lets just say its 8 , co2 comes on Test after an hour ,let's say ph drops to 7.5 measure again after an hour just before lights come on if it reaches 7, that's one ph drop and you are good to go.

At your tank size I'd start with 2-3 bubbles per second max and then adjust up or down.

Ph pens are great tools to achieve this .

I don't know how many bubbles per second mine is because the liquid dried up and I never refilled it, I start 3 hours before, my ph drops more then 1 , I keep an eye one the fish and dropchecker ( it goes slightly yellowish at the end of light period sometimes but fish happy so I ignore it)

Thats my formula took me ages to dial it because I am moron but I got there in the end and I have not touched it since.

Any questions let us know.

 

[hax47]

Fortunately, biology is quite forgiving. Things work within a fairly wide range, so you don't need to be overly precise with your values. I also wouldn't worry too much about the initial period while you’re trying to get the right values. If you aim for 30 ppm, I'm sure you won't notice significant differences if it's 30, 20, or 40.

Surely this fluctuation will cause algae?

I'm not convinced that fluctuations have a significant effect on algae. I've been dosing CO2 once a day for almost a year now with soda water, and the CO2 fluctuates between a maximum of about 30 ppm in the morning and about 3-5 ppm in the evening. I don't think the fluctuations could be much greater, yet I still don't have serious algae issues.

Also any method I can find online requires constant observation/testing, which is unreliable and time consuming, not to mention any difference in initial water parameters such as Kh, water agitation, flow etc can make this even more difficult. Watching a drop checker the entire day, or taking numerous tests doesn't to micromanage everything doesnt seem very reasonable.

These parameters shouldn’t change much during the day/week, so you don't need to monitor your drop checker constantly. Also, with the drop checker, you won't see rapid changes; it needs a few hours to fully equilibrate with your tank's CO2 levels. Start with an initial injection rate, check the drop checker/pH a few hours later, and adjust accordingly. Repeat it a few hours later or the next day until you achieve the desired value.

 

[ian_m]

I use a drop checker and setting CO2 injection rate just takes a few days.

1. Set tank up with drop checkers, filters, power heads, bubble counters, CO2 injection method, light on time, CO2 on times as you would be using when CO2 is sorted.
2. Set a suitable guess at bubble rate, my 180l tank was 1-2bps.
3. When lights come on look at drop checker.
4. If like this fantastic, job done.

5. Just watch it stays the same for all the time the CO2 (and lights) are on.
6. If it looks like this...then whoops, maybe too much. Notice fish not too bothered at this too higher level, as obviously there is oxygen in the water, probably from my plants.

7. Back off CO2 bubble rate and/or increase surface agitation (angle spray bar up in my case) and try again tomorrow.....
8. Once set DON'T FIDDLE. (well don't fiddle too much !!).

 

[Andy Pierce]

Just glance at the drop checker once a day and adjust CO2 if necessary - simples! There is no need to get all fiddly about the levels. It's sort of like with driving a car if someone asks 'how much do you need to turn the steering wheel to turn right?' - try it a bit and you'll get it. To a first approximation CO2 levels are not affected by any other water chemistry parameters. Water flow has an influence, but not a super big one. Having a lid on the tank makes a big difference (CO2 levels will be higher).

 

[bazz]

For me stability is the most important factor, your plants will acclimate to the stable regime that you provide (within reasonable parameters of course) rather than trying to hit some magical number.
Just plant up, it's going to take a week or two for the plants to acclimate to all the other new parameters anyway and it will only take you a couple of days to get the CO2 on song. As long as there is no livestock in the tank it isn't the end of the world if the checker turns yellow for 24 hours.
As always though this is just my take on life.