gpodio

Correct me if I'm wrong but a quick glance at a KH/PH chart will tell me that:

At KH 2,
from Ph 8 to 7 => 5.3ppm difference in CO2
from Ph 7 to 6 => 53.1ppm difference in CO2

So your numbers above are not correct, the equation is indeed linear but because the PH scale itself is not linear, the amount of CO2 required to bring the PH down by 1 unit is ten times the amount required in the previous equation.

So to bring the PH another whole unit lower (to 5) you would need an additional 531ppm of CO2. I think the confusion is because PH is not linear, making the resulting CO2 required also not linear.

Giancarlo Podio

plantbrain

Yes, blah! the pH scale is not linear.
Retract that one

At 0.5 KH the pH would be 5.8 ideally.
Scaling that down to 5 or less is going to get tricky. This part near zero KH is non linear.

It would be easier to remove the KH after getting a reading from the CO2 system. The rate delivery and plant uptake of CO2 should remain similar at both pH's.

But the solubility of CO2 is going to go way down at a KH of zero.
How does that influence the actual CO2 level?

Seems that it will make very tough to dissolve and keep the CO2 in solution to me.

Even if the rate is the same, the actual amount being dissolved will be less. Hence less to the plants.

I wonder how important it is for plants to have a KH at all really.
I mean if they have CO2, Gh etc that's what they care about and what we are trying to measure correct?
Not some pH or KH value really.

But how to accurately measure and maintain the CO2 levels at a KH of zero is an interesting question.

This seems to apply here even at zero KH. But what about this issue of CO2 solubility at a KH of zero with these other cation/anions like Ca/Mg/SO4/PO4/NO3 etc in there?

Carbonates may be a minor component of the buffering system and other acid-base pairs such as phosphates, silicates, borates, and organic acids are predominant. The equivalence point for these pairs is often closer to pH 5.0 than it is 4.5, potentially significant in light of acid deposition in this tank.

I think your best bet is to get a specilized probe but I think you still will have trouble getting a good handle on the CO2 level at aH of zero due to other ion influences in this mix.
Well, talked myself out of that one.

Well, you can also try the Riccia stone approach, when it pearls well after a 2-4 hours after the lights are on, then you have enough CO2 provided there's enough light, PO4/NO3 etc

Use the plants as you indicator which is what it appears like you have been doing anyway, Riccia might be as better plant to gauge the CO2 level.

Do you have a bubble rate?

I'll look into it more. It's a weird but interesting situation and appears to work for you Edward. I'm not going to tell folks to try it mind you, but I wanna know more as a plant torture test and seeing what limits and influences do these parameters really have on submersed aquatics.

Regards,
Tom Barr

Edward

I don't have a choice, lets see what happens.
Well, it is working quite well in the low light tanks with level limiting CO2 reactors that give the same amount of CO2 level all the time. It's made of a jar installed upside down, drilled holes around and kept filled with large CO2 bubble at a constant amount. Any access CO2 escapes to the surface through the holes, not causing any concentration variation. This seems to create stabilized dissolved CO2 level all the time. It's self regulated and it spreads all over the tank even without a pump.


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But in the high light tank with 4 Watts per gallon, the CO2 been pushed in to the pump circulation via a bubble counter. Bubble counters are very unreliable meters regarding CO2 levels. How can we clock 0.8 or 1.2 second per bubble? So this was my only concern. Too little, plants may not be getting enough or too much and thread algae starts showing up. So therefore I needed to measure it somehow.
Yes, it's fun, so why not try it.
How does HCO3 and CO3 increase the solubility of CO2? Do you mean, up to the point of the 4.3 pH limit? Yes, this could be an issue here.
RO is so cheap, it's worth the fun experimenting.
You have mentioned in some post before that it may take plants a week or so to adjust between the choice of taking CO2 or HCO3 instead. What CO2 level is this about? What if the CO2 is weak, lets say 5 to 10 ppm, what will the plant do? CO2 or HCO3?
Watt per gallon

Getting the dolomite wasn't easy. One is powder, too fine for a filter. Second one comes as "pelleted" for horticulture. The dolomite grains are covered in peat and clay. Total loss. So I drove to one of the mines and asked for a sample of screening dolomite. After some sifting I got something like fine sand beach grade.
RO going over this dolomite gives parameters as follows:
pH 8.2 probe
TDS 40uS probe
GH 1.00 Hagen test in 20 ml
KH 2.50 Hagen test in 20 ml
Ca2+ 5.0 ppm Hagen test in 20 ml
Mg2+ 1.8 ppm Hagen test in 20 ml

Not bad, we will see what happens once the tank water gets exchanged by this new supply. Takes time.

I'll be more then happy to try any suggestion you can come up with.

Thank you,
Edward

skids

Tom & Edward, there is a standard ACA (amer. chem assoc) assay for measuring the pH of RO/DI by adding a certain amount of KCL solid to the sample, it gives enough ionic strength to allow a normal glass probe to work fine and accurately. I remember using it in Undergrad inorg chem lab. I'll try to find it this weekend. I suspect you can measure the CO2 by a similar mod to the LaMotte CO2 assay, perhaps LaMotte technical support has both protocols in a faxable form if you ask. These are questions they must get occasionally from water industries.

Edward what temp is the tank maintained at and do you know the max temp a Cardinal will do well at? I found an abstract online that examined cardinal mortaility in shipping from Brazil at different temps, they had no mortaility at 29 and 31 C but total mortality at 35 C and below 19C. I am cranking up a tank of cardnials to accelerate ich removal , but may keep it high for discus eventually.

Any Cardinal breeding?

Tom, Do people still make peat extract by boiling peat and then adding it to water to lower pH ? I have Fluval peat granules in Eclipse 2 biowheel filter but now need to pretreat my 5 g of weekly water change. What's a simple addition guide? I want to get my 25 g cardinal tank to stay at pH 6.4 ish with low kH without CO2 (low light , low maint.) The tap here is pH 8-8.5 <1kH <2gH now. I am interested in acidifing the warm replacement water so a 20% wc doesn't cause a pH/ ionic strengh shift.

Jeff Kropp

Edward,

Have you gotten a handle on the ratio of surface area to tank volume with passive reactors? I thought a 2 inch diameter reactor was about right for a 15 gallon tank. They are certainly helpfull for regulating yeast generated CO2.
___
Jeff

Edward

Sounds interesting, can't wait to try it. Thanks for the info.

Regarding the Cardinals, the tank is at 24C/75F in the winter and very hot during summer seasons. The temperature can go as high as 35C/95F +. I have never lost any fish to excessive heat.
The mortality level you describe, is caused by temperature only at the lower side of the scale, the 19C. But the heat related mortality, in my opinion, is lack of oxygen. There is only very little oxygen in hot water. The fish will be just fine, if you pump lots of air in the water.

My Cardinals are not breeding due to their old age. They are retired now. They are so old, they need glasses to locate food.
You have quite good water over there. Cardinals need KH < 0.2 ppm, GH 1-2, pH < 6.0 (ideal 5.5) and conductivity 10-30 uS. Peat works sometimes well, sometimes not at all. Never know until you try it. Problem is not lowering the pH, but conductivity TDS Total Dissolved Solids. Your KH is so low, that only little of peat will lower the pH sufficiently. That is good, because more peat means more TDS, higher conductivity and the eggs may not like it. You will need to premix it in a separate tank to get the values stabilized for 24 hours. I used to filter water over peat, raw peat, no boiling, no extract. Peat is powerful.

Thank you,
Edward

Edward

I've been using the reactors for a long time, a jar 2.5" in diameter. The advantage is that there is no longer needed any bubble counter and the dissolved level remains stable. But I can not comment on the dissolved concentration yet, as I am still working on a reliable measurement. Preliminary tests show CO2 30ppm in 50 gallon and CO2 60ppm in 4 gallon tank.
What is quite interesting is the fact, that the relatively sensitive electronic pH meter registers equal CO2 spread all over the entire tank even with no water movement, no water circulation, no pump. This is a 90 gallon tank I am talking about.


Thank you,
Edward

skids

Nice reactor could you post a larger macro picture? , don't be too surprized the CO2 is well diffused when at that high of a concentration, the movement of small molecules at 78F in fluid is something like 1000 ft/sec. It's faster from a point source since it's aided by not just browninan motion but also diffusion aided by a concetration gradient and it's very small average diameter of about 0.4 to 0.5 nm.

Did your cardinals spawn without prompting? I.e. separtating males from females few days, feeding lots of live food, then reintroducing? Did they tend to do it at sunset which you allowed to come in from a window? Also did you black out the tank to protect the photosensitve eggs the first three days? Did including a particular plant aid them like Cabomba carolinina, java moss, or Limnophilla sessiliflora which are suggested in a general breeding book I found, help?

MiamiAG

skids,

You blew me away with your comment on CO2 diffusion. Can you expand on that?

plantbrain

Edward,
At low light I can see that a little extra CO2, eg not a lot will make alittle differrence at 0 KH.

But......not enough to whack the pH out too much.
This would also show up as the same pH measurement in the tank.

You mention this does not do well at higher light.

So essentially your going more like a non CO2 tank(or low enrichment).

I think what is going on is the CO2 is moderate 5-10ppm etc, which is okay for low light. Plants will keep using the CO2 down to about 5ppm or so but it relative to the light level which will drive CO2 uptake.

Plants saturate at 30ppm of CO2, etc no matter what light level you have up to full sun.

Having some KH will increase the ability of CO2 to dissolve in water.
HCO3<=>CO2 will hold the gas in solution better. I'm not sure how much this might effect CO2, but something tells me you are not getting at much CO2 into the water as you might think.

Once the CO2 drops pretty low, some plants..............only a few will use the HCO3. There are a couple of ways to do it. Hydrillia does indirect and something like Hornwort will do it on the cell's surface directly.

Most all algae have this ability.

I designed a similar reactor that self levels about 10 years ago. But it's active and uses a powerhead and the bubble gets recirculated by the powerhead's venturi. Once the level reaches the venturi's level, the gas starts dumping out the bottom of the reactor.

This is far more efficient and effective/responsive than any passive diffusion method.

It can also be turned on/off using the light timer.

Since you have no KH this might be useful and easily adapted to your own design. Plant guild makes a copy of my old one that's nice.
I sold some internals in the past, they work great.

0.9 - 1.2 w/gal ain't much CO2 demand..................
I'm thinking with not much being dissolved from no KH, and passive diffusers, this is a soft water non CO2 tank pretty much.

I think at higher light, the bubble method might be good enough for the tank actually.

I know many plant hobbyist in Asia that do it and visually check.
If you use a power head etc to shut it off at night, this might give you better stability.

Just a thought.

Regards,
Tom Barr