using plants that can absorb CO2 at night - anyone tried it?

[frog girl]

So there are several species of Isoetes (high light requirements) that are CAM or C4 plants. This means that their stomata are only open at night so that is when they absorb CO2 & I assume also release stored up oxygen. If these were planted along with regular C3 plants that absorb CO2 during the day maybe it would help both oxygen & CO2 levels stay more constant in a tank with a 24/7 CO2 diffuser going.

Has anyone tried this?? The other name for them is quillwort. I found some online at http://www.azgardens.com/misc_plants.php.

I am definitely thinking of trying this in the shallower warm areas of my pond this summer.

 

[savga]

Sounds like a good idea in theory. Another more expensive solution is to have a refugium that is lit at night to keep O2 an CO2 levels stable. BTW are you a botonist, a college student, or both?

 

[frog girl]

Doesn't the refugium mess up the nigh/day cycle for your animals?? Or does it just contain plants & let water pass in & out while blocking the light??

I am a biologist (adjunct professor at my local Univ.). I study frogs but have a good friend who is a botanist & I love plants. I remembered the C4 stuff from my college ecology course (the prof was the guy who discovered aquatic C4 plants). I have just been trying to solve my nightime pH swings with a DIY CO2 setup & thought this might work. They need a ton of light though & I have a pretty deep tank. I'll probably try them in the pond first.

I suppose I should really be frog woman but I am not planning to grow up. Besides it sounds sort of dorky.

 

[malkore]

If you have a decent Kh (more than 3 degrees) your nightime swings shouldn't be that bad, especially with DIY.
I run pressurized on 3 tanks, 24/7 (except on a water change) and have no problems with fish or plants and the pH change overnight, which is about 0.1 change.

When I do 50% water changes, my pH goes from 7.0 to 7.4 (approx) and I have no problems with the fish and that much of a swing.

Unless you're keeping discus or other VERY delicate fish (german blue rams come to mind) I don't think you need to be as worried about the pH changes.

 

[czcz]

Doesn't the refugium mess up the nigh/day cycle for your animals?? Or does it just contain plants & let water pass in & out while blocking the light??

It can just contain plants, and you could keep the refugium tank underneath the main tank, so gravity helps with 1/2 the water travel (pump returns water to the main tank). If you choose to have a clean-up crew in the refugium and block natural sunlight, I don't think they mind an opposite lighting schedule from the main tank.

I need to experiment, but I think such a set-up may need two CO2 diffusers to be effective, because plants in my set-up only pearl if they're in the same tank as the diffuser. I don't know why. I keep >15ppm CO2 according to Chuck Gadd's calculator, and both tanks measure the same.

I'm sure Malkore is correct and an oppositely lit refugium is unneeded, but they're neat I'm interested in the results if you proceed with the C4 experiment

 

[frog girl]

Malkore,

my pH was going off the bottom of the scale (6 on my testing kit) even with a KH of 10 from 7 to 6.2 in three days. I have been unhooking my DIY CO2 & keeping track of the pH pretty regularly. I think I'm just getting too much CO2 into the tank but I have had a bunch of suggestions of how to fix the problem in another thread & some ideas of my own. Odd that you would have no trouble when you have a so much lower KH & you use pressurized CO2 which I would guess is really efficient. This doesn't quite add up???

czcz,

I wouldn't be suprised if the CO2 comes out of solution when you move the water unless it a really slow gentle flow.

Your refugium looks really cool. I'm not sure I will be doing any C4 experimentation until the spring. As malkore pointed out my tank only really has about 1 W/Gallon so I'm not sure Isoetes would be happy in there. My pond on the other hand gets full sun so I'll probably start out there. I'll try to get some data though & post when I do it.

 

[travis simonson]

frog girl - I believe the Isoetes for sale at AZGardens is I. lacustris. I've got a friend who is growing it in her high-light, non-CO2 supplemented tank with some success. I've got some bunches of Isoetes japonica growing in my high-light, pressurized CO2 125G tank right now. I use a pH controller so CO2 levels remain consistent 24 hours a day. The I. japonica is doing well, but seems to be a bit of a slow grower. Thanks for the info on the CAM/C4 plants. I was unaware that any plants did that

 

[frog girl]

Travis,

I know I need a pH controller but no $$ right now so I have to find another solution.

I'm not sure all Isoetes are CAM plants but I know that lacustris is. Its not too suprising that your Isoetes is growing a bit slow. The CAM/C4 system is not as efficient as regular photosynthesis without CO2 storage but it does allow them to live in some pretty nasty environments. Some plants can actually switch between CAM & normal photosynthesis depending on the environmental conditions. They really can't compete with other plants in terms of growth. A lot of cactus are CAM because they need to minimize water loss during hot days so they don't keep their stomata open except during the nighttime.

Can't really afford more light either . . . well my indoor experiment will probably have to wait a while. Oh well .

 

[Steve Hampton]

my pH was going off the bottom of the scale (6 on my testing kit) even with a KH of 10 from 7 to 6.2

Yikes, if you have an accurate KH reading your starting pH should be about 8.0. Dropping it to 7.0 is as far as you'd ever need to go. However, at a pH of 6.2 your CO2 levels would be about 190 ppm and I'd imagine all your fish would be floating...to that end I believe your KH test result is being interfered with...what is the pH and KH of your tap water, and if that tap water is left out overnight does the pH or KH readings change?

Regarding the need for O2 at night...this shouldn't be an issue when using CO2 injection, the high rate of photosynthesis during the photoperiod usually results in O2 levels that are above 100% staturation. pH stability is unproblematic if it occurs due to changes in the amount of carbonic acid from CO2 levels...within reason, meaning provided CO2 levels don't increase above about 40 ppm. There can be some synergistic affects from a rise in pH related to toxicity of nitrogen compounds and metal toxicity is lightly linked to pH. When pH instablity really becomes dangerous is when it occurs due to changes in GH and/or KH.

 

[frog girl]

My KH which started out at 22 (had a pH of 8.0 then) is now down to 10 & my pH has stopped swinging so drastically its stay at 7 & just beloow. I don't use my tap water because it has so much NaCl in it (we actually get warnings in the summer that folks with high blood pressure shouldn't drink it). In addition we have a water softner which uses KCl instead of NaCl. I have occasionally added a bit of tap water but not much. Before I had such high KH that I only ever added RO. But now that the limestone is gone I should have less of an issue.

I have a regular test kit with liquid reagents so I am not sure what could be wrong.

Based on my now suspect test kit I have never had much nitrogen in the water (I have live plants that goble it up).

I wasn't so worried about releasing the O2 at night as much as hoping the Isoetes would suck up some CO2 to minimize my pH swings.

I really don't know whats going on - I read the chart on the relationship between KH & CO2 & thats part of why I have been trying to decrease my KH a bit because I didn't want floaters.

My fish seem happy though (rasbora, otos, & tiger barbs). They are eating well & playing much more than when the KH was testing out so high.

I am about to change a bunch of things around including part of the substrate so we will see how it all looks when things settle down a bit.