Slow CO2 Buildup Never Reaches Constant

Setup: 125g, freshly light - medium planted, CO2 comes on w/ actinic 45 mins before the 8,000k lights, and stays on with actinic 45 mins after 8,000k lights before it turns off and air bubbles turn on. pH before lights/CO2 on 7.22 w/ KH of 3


Okay, I've only been running my pressurized CO2 w/ my newly build DIY CO2 reactor for a few days now, but... I was expecting my CO2 to increase for a number of hours and then at some point level off and stay fairly constant. Instead, it increases faster at first, and slower later, but just keeps going until it shuts off. My reactor is 100% efficient to the naked eye, and I'm dosing about 1 bubble per 1.25 seconds (medium sized bubble?, 48 bpm). Last night my pH got down to 6.55 before lights/CO2 went out, which is a drop of 0.67. Unfortunately my current drop checker will not stay stuck to the wall and is pretty much useless when it floats away, so I'm approximating my CO2 levels based on pH. I would surmise that my CO2 was getting to somewhere around 25 ppm, maybe less since my Phosphates are still a bit high. I increased my CO2 a little more today, trying to go slowly, to just a tad over 1 bps (67 bpm) so we'll see what that does. But...


Regardless of the specifics, the main thing is it seems to me like my CO2 never reaches a constant. Do others experience this, is this normal? Maybe its not really the CO2, but until I fix my drop checker issue I would assume that it is. Starting tomorrow I also plan to have things setup on 3 separate timers instead of just the 2, so that the CO2 can come on and go off even earlier. Maybe set to come on 1.5-2 hours before the full lights?


Any thoughts would be appreciated, thanks!


David

 

Thanks for the response! Wow, you really think with a KH of 8 a 1.2 drop in pH is only 30?? I would have thought that to be closer to 50 no? I know KH isn't the whole story but still. Already today has been better with a bit more CO2. Without any other way to check levels I'm just going really slowly, but fish are extremely happy so far. Time for a tiny bit more again tomorrow

 

Yeah, it is interesting how the curve has changed already with adding a bit more CO2. I think it's dialed in now to a drop of right about 1, which now happens much faster before leveling off better. I will be swapping out my circulation pump for a more powerful one tomorrow, so I'll see if that affects the surface agitation much or not.

 

At 67 bpm or 1.1 bps I was getting a pH drop of 0.77. I am now currently at 127 bpm or about 2.1 bps, but that should give me more than 1.0 drop in pH. I won't know exactly until tonight, as I've been adjusting it slightly everyday, but I got a drop of 1.01 pH yesterday with slightly less CO2, probably just under 2 bps. My KH was at 3 at the time, I've now brought it to 4.5.


Are you guys getting 100% CO2 dissolution as far as the eye can tell? I made my DIY reactor 2' long, plus end caps, making it 28" total. I also don't use spray bars or such, but my lines are all drilled into the back of my tank on the lower half / third. Not getting a lot of surface agitation currently, but the new circulation pump that's going in might increase that some.


Another thing to consider is these plants have only been in here for a few days, so may not have fully adapted yet, and may not be using much CO2 yet. Don't really know, just a thought? Last of the plants coming this week.


Also, I know a bunch of different tank dimensions are lumped into the same standard sizes. My tank, being 5x1.5x2 is actually just 15 cu ft, or just over 112 gallons in actuality. After substrate, rock cave, drift wood, etc. I dunno, maybe 100 gallons of water if fully topped off? Also, I didn't think to mention that I was messing with stuff at the time, so the tank wasn't full, but had about 84 gallons in it (I added 16 gallons to top it off last night). Still, 84 out of 125 is still 2/3 of what you guys thought, and from the sounds of it that's still far from what you were expecting, which is why I ask about your setups? Again, drop checker is still out of commission since I can't figure out how to get it to stay put. Will need to find a better suction cup that fits it or buy another one if I care enough, so basing all this off of pH drop, so don't know exactly what CO2 levels are, but they must be decent for that kind of drop w/ any KH over 2.5.

Holy crap, seriously? Are there fish in there? Do you know the actual CO2 levels?


jrneuzil - KH of 22? Wow. That's gotta change things significantly I would think, but I'm new to CO2, so not really sure how much of a change to expect there.


Thanks for the input everyone!

 

As for my pH, I test using a Pinpoint pH monitor in the tank at all times. Yesterday I pulled it out, cleaned it, and calibrated just to be sure, but that changed nothing as it wasn't dirty or out of whack. I didn't get a pH drop of 1 until I had about 2 bps with less water in the tank and a KH of 3. Now that I've raised my KH a bit and the tank is full, along with a bit more surface agitation from the new pump I put in last night, I'm currently trying 194 bpm or 3.2 bps. I've also got my 3 separate timers setup now, so the CO2 is coming on 2 hours before the lights and going off 2 hours before the lights. This should be better for the plants, and theoretically will increase the amount of CO2 a little bit faster as the plants aren't yet using it up, plus everything they are giving off during lights out is no longer being wasted by the aeration. I don't expect that to mean much right now, but when the tank is more heavily planted and the plants have adjusted and are growing faster it will play a small role.


I would have to guess that your experience differs from mine for 5 or more possible reasons.


1. Bubble size. If my bubbles are twice as big as yours then we're injecting the same amount of CO2. If yours are twice as big then you're injecting 4x what I am. This is probably the biggest unknown and why comparing bps isn't necessarily helpful.


2. How is CO2 measured? How are you measuring your CO2? Are you also just looking at pH drop? I unfortunately am only getting an idea of my CO2 levels based on my pH drop, and without having checked actual CO2 levels with another method before on my water parameters, I can't really say how much CO2 I have, only that it's fairly significant as my KH is above the crucial 2.5 mark and is dropping over 1.0.


3. KH levels. My KH is around 4.5. If your KH is much higher, such as 22 like jrneuzil's, then your pH won't drop nearly as fast, or rather to get the same pH drop you'll need a lot more CO2.


4. CO2 dissolution. This is an important one, because while many people like myself are using a reactor that can get what looks like 100% CO2 dissolution, others are using methods that hardly work at all. Many many years ago I remember trying one of those step ladder things which maybe had 50% dissolution at best. I also tried plugging it into my Maxi-Jet 1200 to chop up and spit out smaller bubbles, and while I can't say what % effectiveness that was I can say it wasn't great. I wasn't even going to attempt a lusher planted tank unless I had a great CO2 dissolution method, hence why I just built the reactor (and am super happy w/ the results).


5. KH is a measure of buffering capacity, but that alone doesn't say what the buffer range is. If just measuring pH drop, comparing your KH to another's isn't necessarily accurate. Buffers have an effective working range. If you're not adding that buffer than you likely have no idea what the buffer is made up of and it may not buffer well in the pH range you're using. If you use commercially bought buffers then they should state the pKa from which you can infer much about the buffering capacity. If using something of your own, such as Potassium Carbonate, it will raise your KH but the pH buffering range is higher and might not do much to stabilize your pH at typical planted aquarium levels of 6-7.


The biggest issue with KH is for those that have levels below 2.5, as this is when big sudden pH swings can come into play. KH, as well as GH and pH, will all drop over time, so especially for those with low KH tap water and who don't do water changes fast enough, this can be a big problem. Adding buffers / KH is simply a must for many people, but for those with enough in there water naturally it is often a non issue.


I've been keeping fish for over 12 years in a 55, 125, and 25 gallon sizes at times. I'm surrounded by chemists, engineers, and doctors, so it's always fun to have in depth discussions about chemistry and flow patterns and such. I am new to plants however. I've had a few PetsMart plants that weren't even true submersible plants in the past, but this is my first attempt at a full on planted tank. I've been researching it for years slowly getting the different pieces of equipment I wanted for this venture and soaking up all the knowledge I can, and I'm super excited that the time has finally arrived if you can't tell.

 

6. I forgot to mention the obvious - surface agitation. This varies greatly from one tank setup to another. I would say I have little surface agitation compared to many people, while others have hob filters or even spray bars that shoot in from above the water line. This would be quite a difference in the amount of CO2 you'd have to pump in to get the same levels as it would be escaping at a faster rate as well.

 

Ah, so that's your old tank info then I take it. Do you still have a heavily planted tank with the same pressurized CO2 setup? I know a lot of things changed obviously, but just wondering if you noticed a big change in your pH drop (assuming you are going off a constant and measured amount of CO2)? Maybe too many variables to make a worth while comparison, but a KH change of 13 makes me curious.