# Co2: 2 hours before lights turns on. Why?



## Cor (13 Nov 2017)

When I'm doing research everywhere I go it's the same advice: two hours before the lights turn on you start dosing the CO2. So when the light turn on there is the right amount of CO2 in the tank.

But why *two* hours?
Isn't it depending on the size of the tank and the amount of ppm?
An tank of 50 liters for example, only takes 1 hour to reach the determined levels. In 500 liter tank maybe needs about 5 hours. So why keep I reading just 2 hours before lights.  Please someone can explain this.

Cheers, Cor


----------



## Edvet (13 Nov 2017)

https://www.ukaps.org/forum/threads/browning-and-melting-hc.51188/page-3#post-504510
in short: CO2 has to be up and running when the light goes on, and better be sure about it. Best way would be do a pH profile  pH has to be lowest when the lights go on.


----------



## Zeus. (13 Nov 2017)

In my 50l tank it tanks three hours to hit target pH drop. But in my 500l tank I get the same pH drop in less than 75mins, but the 500l has twim inline atomisers and twin reactors and one high BBS. Plus one of the atomizers switches off once target pH is reached.


----------



## ian_m (13 Nov 2017)

You are forgetting that the bigger the tank the greater the loss of CO2 due to a greater surface area, thus a bigger tank will require a higher injection rate to both get CO2 into a larger volume of water and to make up for larger losses due to increased surface area. A large % of the CO2 you inject escapes away, maybe 80-90%.

What you are trying to acheive is that at lights on the CO2 injection rate matches the CO2 loss rate, as hopefully at this time no more CO2 is dissolving in the water.

You can inject faster for a smaller tank, if you want to, to reach say 30ppm quicker in say 1 hour, but you must also have a greater loss rate or else ppm will over shoot 30ppm very quickly.

Similarly you could inject slowly if you have a low loss tank, but as you are injecting slowly it may take many hours to get to 30ppm.

The graph below shows how CO2 rises for a slow, OK and fast injection rate, cleverly setup and balanced to acheive 30ppm after 2 hours. The clever bit which is where the CO2 mastery comes from is managing to get the 30pm (or 1pH drop) by the time the lights are on.





It appears then as a rule of thumb, the injection rate to acheive the mystical 30ppm (or 1pH drop) takes two hours on a typical surface loss tank. Unless you are Zeus with a monster tank and two injectors and clever control system.


----------



## Tim Harrison (13 Nov 2017)

Yep there are many factors...2 hrs is really just a guide. Mine comes on 3 hrs before, that way I get lime green at lights on and it stays that way - stable - throughout the photoperiod.

In other words the rate of injection is the same as the rate it's used up by the plants photosynthesising during the photoperiod. it's basically a balancing act,

Put another way, in order to get lime green at lights on after 2 hours I'd have to increase the injection rate to the point where CO2 concentration would continue to climb during the photoperiod which would eventually gas my critters.

So in a nutshell the start time determines the injection rate, which in turn determines the CO2 concentration throughout the photoperiod.


----------



## Kallor (13 Nov 2017)

Tim Harrison said:


> Yep there are many factors...2 hrs is really just a guide. Mine comes on 3 hrs before, that way I get lime green at lights on and it stays that way - stable - throughout the photoperiod.
> 
> In other words the rate of injection is the same as the rate it's used up by the plants photosynthesising during the photoperiod. it's basically a balancing act,
> 
> ...



interesting when do you stop your c02 when the lights go off or a hour or two before? ,currently my c02 comes on one hour before the photo period lights come on at 2pm drop checker is green by 3 pm c02 off at 9 light off at 10 i might try putting the c02  on at 12pm and off 8pm


----------



## Zeus. (13 Nov 2017)

CO2 off two hours before lights off is the general rules most folks use as the plants have had their fill and in the last two hours the pH will remain pretty stable. Having the [CO2] at optimal levels when the lights come on is most important to help prevent algae issues, best if you can have lower light intensity for the first 30mins as the plants get ready to photosynthesis at there full rate. Plus less light for alge to take advantage off when the plants can use the light to their max. then keep the [CO2] stable throughout the photo period esp the first 4hrs. If your DC turns yellow 3 hours into photoperiod you [CO2] is constantly rising which isnt good. A pH pen can be a cheap way to test your pH and the relative stability of the [CO2]. Fluctuating [CO2] is bad as the plants do much better if the [CO2] is the same throughout the photoperiod ( first 4hrs) and day to day.


----------



## Kallor (13 Nov 2017)

great tip thanks Zeus been having some brown algae issues mainly collecting on my foreground plants since i re started up the co2 a couple of weeks ago i'll adjust the c02 times to try and cure it. was thinking of buying this pen


https://www.amazon.co.uk/Semlos-Res...ie=UTF8&qid=1510597794&sr=8-3&keywords=ph+pen


----------



## Zeus. (13 Nov 2017)

Kallor said:


> great tip thanks Zeus been having some brown algae issues mainly collecting on my foreground plants since i re started up the co2 a couple of weeks ago i'll adjust the c02 times to try and cure it. was thinking of buying this pen
> 
> 
> https://www.amazon.co.uk/Semlos-Res...ie=UTF8&qid=1510597794&sr=8-3&keywords=ph+pen



Think thats the same one I got to backup my pH controller, dont get to hang on on the actual pH as a £12 pH pan will not be accurate. But it will enable you se see if the pH is stable over the photo period, doing it every 30mins and making a note of the reading. Will also give a reasonable idea of what pH drop you are getting. As long as you take the pH of the tank water before the CO2 starts. One of the limits of the pen is you can not put move it all over the tank to see if the pH is similar all over from just above the substrate to dense areas of plants. Your limited to the relative surface of the tank. The next day you use it its readings may not be the same pH as they soon need recalibrating.


----------



## Cor (13 Nov 2017)

So, if I understand correctly, the 2 hour time frame is an average approach.

If the injection rate is to fast the CO2 levels would increase the ppm CO2 to dangerous levels in time. So I must adjust my surface agitation to compensate the 30ppm... (?)


----------



## Zeus. (13 Nov 2017)

Cor said:


> So, if I understand correctly, the 2 hour time frame is an average approach.
> 
> If the injection rate is to fast the CO2 levels would increase the ppm CO2 to dangerous levels in time. So I must adjust my surface agitation to compensate the 30ppm... (?)


Yes, 2hrs is the average, each tank is different.
A low BPS may take 4hrs to get the right [CO2] and then remain stable. However  a higher BBS may only take say 90mins but then keep increasing, but by having better flow and/or surface aggitation CO2 will be lost faster and the higher BBS will max out faster at a lower [CO2] and remain stable easier, plus the better flow helps get the [CO2] even in all the tank.
Dennis Wong has some great vids on YouTube on CO2 explaining this approach, well worth a watch IMO.
Getting the CO2 injection rates right is difficult. Also getting it so [CO2] doesn't fluctuate is is also tricky. But to get the most out of CO2 without issues both must be done well. Along with ferts and light intensity.
When you add CO2 to a tank it takes 2/3 weeks for the plants to adjust to it and light levels should be kept low for that period and then slowly increased. Don't be tempted to increase the light to get pearling too fast, it will pearl if you do it too quick, then aglea will follow and plant damage.
Plus with CO2, extra light your plants will consume more nutrients so that may need adjusting too or algea and plant damage may result also.

Hope it helps

Zeus

Sent from Mountolympus via neural interface


----------



## ceg4048 (13 Nov 2017)

Cor said:


> So, if I understand correctly, the 2 hour time frame is an average approach.
> 
> If the injection rate is to fast the CO2 levels would increase the ppm CO2 to dangerous levels in time. So I must adjust my surface agitation to compensate the 30ppm... (?)


Hello,
       Yes these statements are correct, but it is important to understand the fundamental basis of the gas timing.
It would be helpful if you could take pH readings of the tank from just before gas on until lights off. You should take pH reading at least every hour and probably every 1/2 hour for better accuracy.

Have a read of the thread https://ukaps.org/forum/threads/melting-marsilea-hirsuta-staurogyne-repens.28996/ to get a better understanding of why 2 hours is a typical number. As mentioned by other posters, there are a lot of variables, but you need to find the correct timing for your particular tank and not just use an average number.

By analyzing the pH profile along the photoperiod you can identify problems or can confirm that the injection technique is correct.

Cheers,


----------



## Cor (14 Nov 2017)

Many thanks for this useful explanation, much appreciated 



Zeus. said:


> Don't be tempted to increase the light to get pearling too fast, it will pearl if you do it too quick, then aglea will follow and plant damage.
> Plus with CO2, extra light your plants will consume more nutrients so that may need adjusting too or algea and plant damage may result also.



Perhaps you can confirm:
way too much light along the photoperiod will damage the cell structure of low-light plants?
That is why you'll see a string of bubbles O2 escapes the plant tissue?


----------



## Edvet (14 Nov 2017)

Cor said:


> way too much light along the photoperiod will damage the cell structure


Of all plants


----------



## Zeus. (14 Nov 2017)

Cor said:


> That is why you'll see a string of bubbles O2 escapes the plant tissue?



Yep been there with Crypts, then weeks later sometimes even months holes appear in leaves and to late for whole leaf damage is done. Holes get bigger and more off them if left in tank.


----------



## Cor (14 Nov 2017)

Last question: I've been told that this kind of damage will release glucose into the water and presumably can cause algae.
Any info about that?

sorry for all the questions. But with every answer a new question is popping up


----------



## Edvet (14 Nov 2017)

I don't think releasing the bubbles has to do with plant damage, it's something which can be seen with perfectly healthy plants. The oxygen gets released through the surface cells.
The holes in the crypts  would point to damage through light/CO2 deficit.
Glucose shoudn't cause algea. Dropping sugar in a healthy aquarium doesn't cause algae. Damaged plants cause algae because algae cope far better with suboptimal conditions and outgrow the plants.


----------

