Does this feel right for CO2 ramp-up?

[Bradders]

Hi CO2 experts,

So, my 250L aquarium project is ongoing. Fully planted, CO2 injected with inline atomiser, Oase 850 filter. Lilly-pipe glassware and a WRGB2 Pro light. So far so good! Nothing is more than 5 weeks old.

My question is about the time it takes to ramp up to get to the right CO2 levels. With the 1pH drop rule, I am pumping CO2 into the aquarium for about 4-5 hours (at 5bps) to get near that mark. So much literature is saying 2-3 hours so I started wondering whether 5 hours is really an indication that something is not quite right? 250L is big, but its not that big!

I do have some surface agitation from the lilly pipe (as below) and I can tell you the off-gassing does seem to be fairly fast once the CO2 is off. Suggesting that there is a good gas-exchange. But should a 250L tank really take 5 hours to reach the target when injecting 5 bubbles a second?

Any advice would be greatly appreciated!

Brad

 

[LMuhlen]

While I don't have much of a personal reference to give you, my understanding is that you would need to have more surface agitation and more CO2 injection to quickly, but safely, reach your concentration goal. Keeping injection slow and surface agitation low leads to a slow ramp up that may keep ramping up after the lights are on if you don't pay attention and adjust the timings.

 

[Bradders]

While I don't have much of a personal reference to give you, my understanding is that you would need to have more surface agitation and more CO2 injection to quickly, but safely, reach your concentration goal. Keeping injection slow and surface agitation low leads to a slow ramp up that may keep ramping up after the lights are on if you don't pay attention and adjust the timings.

I don't think I have the problem per se. I seem to have moderate surface agitation and a 5BPS injection rate and still a slow (5 hour) ramp-up and not make it quite to 1pH.

 

[FrozenShivers]

BPS doesn't mean much on it's own as it isn't a calibrated constant across brands, so for example 1BPS across different setups won't equate to the same amount of CO2 being injected. How long does it take for your drop checker to reach green? I think there's around a 1-2 hour delay from real time.

 

[LMuhlen]

I don't think I have the problem per se. I seem to have moderate surface agitation and a 5BPS injection rate and still a slow (5 hour) ramp-up and not make it quite to 1pH.

Not reaching the desired pH drop and having an excessively long ramp up indicates to me that you need to add a lot more CO2 and possibly increase surface agitation. Start adding more CO2. If you find that the CO2 keeps ramping up significantly after lights on, then you need more surface agitation to reach stability quicker. If it increases degassing? More CO2. Until you reach the point where you get the desired pH drop at the desired time frame.

To increase CO2 dissolution, you may need to review your equipment configuration, other than increasing the gas rate. Are you using a diffuser? Reactor?

Bubble count may also be affected by the gas pressure, which affects gas density. Other than the gas density, different geometry in the bubble counter may lead to different bubble sizes. Lots of variables. Bubble count is more of a self-reference thing to see if things are working stably, and less of a way to compare to others.

 

[Bradders]

To increase CO2 dissolution, you may need to review your equipment configuration, other than increasing the gas rate. Are you using a diffuser? Reactor?

Inline diffuser.

Not reaching the desired pH drop and having an excessively long ramp up indicates to me that you need to add a lot more CO2 and possibly increase surface agitation. Start adding more CO2. If you find that the CO2 keeps ramping up significantly after lights on, then you need more surface agitation to reach stability quicker. If it increases degassing? More CO2. Until you reach the point where you get the desired pH drop at the desired time frame.

At present, the CO2 comes on 5 hours before the lights do. Moves from a pH of ~7, to a pH of ~6.32 when the lights come on. It then stays pretty steady (6.31 to 6.32). In short, long ramp-up, not quite 1 full pH but steady when the lights come on. To give an idea of off-gassing (when CO2 stops, it has just moved from 6.32 to 6.52 in around 2 hours. By the morning, it will settle around 7pH, as that is where soil currently buffers my water. (Tap water usually around a pH of 7.5).

So, it sounds like (if I hear you correctly) i need to up the CO2 and potentially up the surface agitation. But do I also need to think about reducing the 5 hour ramp up?

EDIT: Another thing is that my plants are pearling a bit, and the drop checker is a shade of green - that expected with a ~0.7 pH drop?

 

[bazz]

If you're looking for a fast pH1 drop in a 250l tank you're going to use a lot of gas, this is Zeus's 500l tank but you'll get the picture Olympus is Calling.

 

[Bradders]

If you're looking for a fast pH1 drop in a 250l tank you're going to use a lot of gas, this is Zeus's 500l tank but you'll get the picture Olympus is Calling.

Out of interest (being new to this) is there a difference between a fast drop to target, verse a slow drop to target? My head tells me it would be the same amount of gas but I think I am not right.

 

[Zeus.]

Dialling in the CO2 injection Rate and CO2 Profiles - worth a read and covers the topic.

The rate of the pH drop is out off your control with single injection and is dependant on many factors esp the pH drop itself. One you have a stable pH the time it takes is the time it takes for every tank.

I used dual injection with dual timers, solenoids, CO2 reactors etc so after target pH was reached ( well just before) one injection was turned off. Using dual injection makes it very easy, but costs in equipment.

Another very exciting option is the Yugang reactor, which is in production and can be shipped from the states. Users have reported fast/impressive results. I would try the product myself if I had a suitable project.

 

[dw1305]

Hi all,

.... and the drop checker is a shade of green - that expected with a ~0.7 pH drop

Obviously not a CO2 user, but I've had a lot of experience with pH meters and I'd be <"happier to trust the drop checker">.

Another thing is that my plants are pearling a bit

This just means the water is saturated with dissolved oxygen and the "excess oxygen" is outgassing as "pearling" (O2 bubbles). It is a pretty good indication that you have sufficient CO2 (and mineral nutrients) available.

During photosynthesis one molecule of oxygen (O2) is evolved for every <"molecule of CO2 incorporated">, so pearling is a pretty good (indirect) measure of CO2 availability.

cheers Darrel

 

[LMuhlen]

At present, the CO2 comes on 5 hours before the lights do. Moves from a pH of ~7, to a pH of ~6.32 when the lights come on. It then stays pretty steady (6.31 to 6.32). In short, long ramp-up, not quite 1 full pH but steady when the lights come on. To give an idea of off-gassing (when CO2 stops, it has just moved from 6.32 to 6.52 in around 2 hours. By the morning, it will settle around 7pH, as that is where soil currently buffers my water. (Tap water usually around a pH of 7.5).

I see comments from people who track their pH profiles in a more precise way than I do, that the tank doesn't fully degas during the lights off period. So I would recommend that you further investigate the base pH of your water, especially since that is very relevant when using the 1pH drop strategy. It is possible that the pH 7 starting point is not the fully degassed point, meaning that you are indeed closer to the 1 pH drop mark that you are seeking.

Try leaving a sample of tank water for more than a day, or to vigorously aerate it, and see if you can reach a pH higher than 7.

 

[Bradders]

I see comments from people who track their pH profiles in a more precise way than I do, that the tank doesn't fully degas during the lights off period. So I would recommend that you further investigate the base pH of your water, especially since that is very relevant when using the 1pH drop strategy. It is possible that the pH 7 starting point is not the fully degassed point, meaning that you are indeed closer to the 1 pH drop mark that you are seeking.

Try leaving a sample of tank water for more than a day, or to vigorously aerate it, and see if you can reach a pH higher than 7.

I think that is what is confusing me somewhat. If I vigorously aerate the tank water (pH7), it kind of gets closer to the tap water. (ph7.5+). Which is expected, as the the tap water is 7.5, and the buffer in the water makes it 7 in the tank.

I was told it relative to the water in the aquarium, which is buffered at 7. So am I going wrong somewhere?

 

[LMuhlen]

My understanding is that buffers are molecules dissolved in the water, they are not the substrate itself. The substrate may release a buffer to the water, but the most common thing is that it absorbs the carbonates that buffer the water to a higher pH, reducing their concentration and therefore reducing the pH. The water itself doesn't change when removed from the tank to make your sample, it already has been affected by the substrate in whatever way it acts. When you aerate, you simply change the CO2 concentration and move it closer to the equilibrium with the air. It is possible that there are other gases at play, but I don't think this is what is happening here, from what I understand we are only talking about ions from solid salts.

Now that I think of it, if the substrate is playing some game of release/absorb carbonates depending on the pH, then this makes it impossible to use the 1 pH drop strategy. This strategy assumes constant alkalinity in the water. Then I would defer the answer to someone with a better theoretical knowledge on the matter.

I see people often assuming the substrate only absorbs carbonates until it saturates, but who knows what those crazy aquarium industry people are doing...

 

[Zeus.]

I was told it relative to the water in the aquarium, which is buffered at 7. So am I going wrong somewhere?

The tank water and the tap water will not have the same degased pH in a planted tank, as the substrate and rocks/wood/ferts etc change the parameters of the tank water.

A tank without substrate/rocks etc the tank water and tap water would be the same - until you add anything

 

[Bradders]

The tank water and the tap water will not have the same degased pH in a planted tank, as the substrate and rocks/wood/ferts etc change the parameters of the tank water.

A tank without substrate/rocks etc the tank water and tap water would be the same - until you add anything

Which makes sense. So, I have tap water at 7.5, tank water at 7.0 due to substrate buffering, and pearling at 6.3 with a lime green drop checker. Considering that a full pH should be 6 using tank water as a reference point, that is my confusion. Is that because the drop checker has a pretty broad range of ‘green’?

(I know Darrel and others are saying trust the drop checker, just want to understand the science).

 

[Maf 2500]

If you take a jug of pH 7.0 water out of the tank and let it sit for at least 24 hours, what value does it stabilise at? This value would be where you need to measure your pH drop from, not water straight from the tank. Of course it might also be 7.0, but more likely it will be a little higher.

 

[dw1305]

Hi all,

.... Is that because the drop checker has a pretty broad range of ‘green’?

It does, the colour is due to the mix of protonated, and deprotonated, bromothymol blue molecules.

When all molecules are deprotonated the colour is blue and when they are all protonated yellow, if you have a mix of blue and yellow? You have green.

Acids are proton (H+) donors, the source of the protons is the small proportion of added CO2 that becomes H2CO3 and that has disassociated into a proton and a HCO3- ion

(I know Darrel and others are saying trust the drop checker, just want to understand the science)....

Fair enough.

Cheers Darrel

 

[Zeus.]

(I know Darrel and others are saying trust the drop checker, just want to understand the science).

Just give it more time for sample to degas - even more than 24 hours

Like @dw1305 I trust the DC

 

[Bradders]

Just give it more time for sample to degas - even more than 24 hours

Sample degassing as we speak!

 

[Zeus.]

Another trick to make sure its degased is to put the sample in a container the DC can be fitted in - when its very blue its degased. My 50 litre tank took at least a couple of days to go blue with no CO2 injection