O2 vs CO2

[javajo]

Good morning -

Assuming my readings are correct -

PH - 6.0-6.4
KH - 2 degress

My CO2 ranges from 23.8-60ppm.

This is without injecting any additional CO2

I do plan on raising my KH/PH slightly by adding baking soda.

I've heard that plants like still water and that the airstones should be kept to a minimum. (I have two going at full blast on either side of my tank powered by a TetraTec air pump with adjustable air flow.

Should I turn these airstones down a bit? If I do, I'm going to decrease the O2 and increase CO2 which could be harmfull.

I may want to consider turning down my O2 flow once I raise my KH/PH a bit. That way, my water will be more stable, and I should effectivley decrease the natural CO2 in my tank.

Sorry for rambling on - anyone have any thoughts?

 

[Lateral Line]

Air stones do not directly add O2 to the water, they disturb the surface, which is where the O2 dissolves in, less surface movement, less gas exchange.

That said, if you are planning to inject CO2, you will want to reduce your gas exchange, because CO2 comes out of solution VERY easily. If you have an airstone running, you will pretty much loose any benefit from your CO2 injection.

Unless you overstock, dropping the airstones completely will not cause problems. A gentle surface movement from a filter return is more then adequate.

The CO2 concentration in the water does not reduce the O2 concentration. A common misconception is that High CO2 MUST mean low O2 - this is not the case. Both have their own solubility product in water of a certain temperature.

Some plants like still water, others grow naturally in moving water. No simple answer there I'm afraid.

 

[Magnus]

Ditto on LL's reply, I just wanted to add a little more.
I don't think you have more than 3ppm of CO2 in your tank right now. Either you water is extremely soft, or the test kit is wrong. Without CO2 injection, having aerators may actually increase your CO2 level a little bit. You can leave them on, but I think the out flow from your filter is enough (unless you have canister filter where the outflow is at the bottom of the tank). Most plants prefer a little current. It helps bring the nutrients to the plants and also makes it easier for plants to use CO2. I'm sure your fish will enjoy a little current too!
HTH.

 

[javajo]

Thanks for the feedback!

I don't think you have more than 3ppm of CO2 in your tank right now. Either you water is extremely soft, or the test kit is wrong.

KH - 2
GH - 9

PH - Anywhere from below 6.0-6.4

Are you saying that in my case the CO2 chart does not apply? - Are these numbers impossible?

 

[Bol]

Are you saying that in my case the CO2 chart does not apply? - Are these numbers impossible?

Hi, again, javajo. My answers to that would be "most likely, and with 'normal' water, yes".

Those numbers may not be impossible, but seem extremely unlikely. They seem to indicate that you have a CO2 concentration of 24-60 ppm without injecting CO2, and the 'natural' level of CO2 in 'normal' water (that's in equilibrium with atmosphere) is 3-4 ppm.

If you did have 24-60ppm CO2, and were not injecting any, then under normal conditions it would almost certainly outgas pretty quickly, and within a short period of time (day or so?) you'd find that your CO2 would be down to 3-4ppm.

Remember, the standard CO2 chart only works if the only buffers present in your tank in significant amounts are carbonates. Toss in other buffers, such as phosphates, and all bets are off, as far as that calculation goes.

In effect, I would guess that you have some sort of acid in your tank, that's fairly constantly being added. The two most common culprits are a) certain types of driftwood, which will release tannic acids, and b ) high (over 1ppm) levels of phosphates in your tap water. (A third source would be excess nitrates, but I remember you keep those in control).

 

[Lateral Line]

Just an observation, CO2 levels of 60ppm are actually toxic to some fish, in fact, 40ppm is certainly as much as you want to aim for.

I wish my normal water supply was as soft as yours.

 

[javajo]

Thanks again -

Hey Bol - how are you -

In effect, I would guess that you have some sort of acid in your tank, that's fairly constantly being added. The two most common culprits are a) certain types of driftwood, which will release tannic acids, and b ) high (over 1ppm) levels of phosphates in your tap water. (A third source would be excess nitrates, but I remember you keep those in control).

I currently have no driftwood - I am in the process of soaking a nice piece of Malaysian drift wood to add to my tank. Trying to soak for at least 2 weeks so as to avoid leaching tannin into the water and "browning" it up.

I wish my normal water supply was as soft as yours.

Could it be that my water is just naturally low in KH? - I should test my tap water.
I do keep alot of fish as you can see in my signature, so that might account for the low PH. I'm sure I also have some dead leaves on my sword that are contributing to the acidity.

Might be a combination of a naturally low KH & lots of fish?
I still need to add the baking soda I bought last week to try and raise my KH/PH. I keep on putting that water change off.

 

[Lateral Line]

>>> I should test my tap water.

May be a good move, at least then you know what you are starting with. If the tap water is similar to your tank water then there is nothing pulling it down.

Water that soft from the tap is unusual, most water companies harden it as acidic water corrodes metal parts in pumps, pipes and valves.

You certainly have an awful lot of fish in that tank.

 

[Sang72]

When you add CO2 to H20, you get in small quantities H2CO3 (carbonic acid)

This is what gives sodas that sharp taste.

Fortunately H2CO3 is not very stable and dissapates rapidly, so there is not a buildup of acid.

I have a CO2 system, it dropped my PH to about 6.4 from 6.8

I use arrowhead mountain spring water to bring the PH up if necessary. It contains bicarbonates and tests about a PH 7.8

 

[javajo]

You certainly have an awful lot of fish in that tank.

Perhaps that's the problem. The nitrification process is in overload causing alot of hydrogen ions to be added to my tank water. Excess hydrogen would bring the PH down.

The funny thing is it doesn't seem like alot of fish. Most of them are rather small (under an inch.)

 

[Great Lakes]

In some cases of people living in newr homes. lack of fresh oxygen is a contributing factor. I have heard of people raising their ph levels by half a point by opening a nearby window.

Don't know if this applies though....

GL

 

[Bol]

Eep. I forgot from your last thread that you haven't tested your tap water yet. Like LL said, I'd test that asap -- may save a lot of head-scratching.

You do mention that your nitrate levels stay below 30. I'm not sure that a level that low would contribute to a pH drop noticeably. Could be wrong, especially with that low a KH. I've found no measureable difference in pH with nitrates at 10 ppm and at 40 ppm, but I've got pretty hard water (pH 8.0, GH 19, KH 10).

Also, if you're concerned about overstock, one thing that may help you is to test your nitrates a few minutes after a significant water change (25% or so), and then see how fast they rise.

 

[javajo]

Thanks again for the responses -

Also, if you're concerned about overstock, one thing that may help you is to test your nitrates a few minutes after a significant water change (25% or so), and then see how fast they rise.

OK - Here's what I understand -
A byproduct of the nitification process are hydrogen ions (acid) that are normally buffered by alkaline water. Alkaline water contains sodium bicarbonates. The more alkaline your water is the more sodium bicarbonates are present. The more alkaline your water is, the better your water's buffering capability which equates to stable water without frequent PH shifts. Am I correct?

Adding on to this thought - if the nitrification process produces Hydrogen ions as a by-product, Could you say that Nitrate, which is the final by-product of the nitrification process, contains Hydrogen ions?

If this is the case, then perhaps my overstocked tank is prodcing high acid levels due to the fact that it's pushing the tank to nitrify more fish waste, thereby causing high levels of Nitrate and Hydrogen ions?

Either iv'e totally gone over the edge or I'm about to crack this whole thing wide open.


OK - things to do tonight:

Test KH and GH of tap water
Do water change
Add baking soda to raise KH/PH

 

[Lateral Line]

>>> Test KH and GH of tap water

... and pH.

 

[waterwatereverywhere]

Remember, the standard CO2 chart only works if the only buffers present in your tank in significant amounts are carbonates. Toss in other buffers, such as phosphates, and all bets are off, as far as that calculation goes.

Worth testing phosphates, I'd suggest - my phosphate test kit reads up to 5ppm, and my tap water goes off the scale on it!