KH and co2 effects

[tiptoptank]

So first off I have really hard tap water. kh of about 10. But the second I add it to my tank It goes to about 3 or sometimes 2. Now I have a presurised c02 and was wondering if the co2 acually removes the carbonates or are the plants and drift wood absorbing the KH. This is a problem because my PH goes to about 6.6 - 6.7 during the day and thats right on the line of to low.

I add some sea buff to get the Ph back to normal but was wonding if thats having ill affects on the co2. Can I be adding anything to my water changes to rectify this Ph problem?

 

[travis simonson]

I keep plants in my African cichlid tank and have to buffer the water to keep it hard for them. I use sodium bicarbonate (plain old baking soda) to increase the KH/pH at water change time. I don't have the forumula but I know that a solution of 4 TBLSPNS baking soda in 1000 mL of water will yield a mixture that will raise the KH in my 125G tank by 1 dKH per 100 mL of solution added. This also, by necessity, increases the pH of my water, but in no way effects the CO2 content. You just have to keep an eye on your KH when it comes time to figure out CO2 levels. Hope this helps

 

[TankGirl]

Increase your water changes (KH will drop in pressurized CO2 tanks - I need to find that reference) to keep your KH up or simply back off on your CO2 bubble count. Do you have a pH monitor?

 

[jsoong]

I like tyo see that reference TG ... My physiology texts would say that CO2 will not drop HCO3 level (KH) ... after all CO2 + H2O -> HCO3 + H+, that gives you more HCO3, not less.

A drop from 10 to 3 is rather drastic ... any chance of something in the tank interfering with the test? ... or some source of acid?

EDIT: - TG - Reread the first part of this post & it looks a bit snobbish! not intended .... Just that my understanding is that CO2 should not cause a drop in KH ... If there is a reference to explain why it should, I would like to see it ... as I find the whole water chemistry fascinating.

 

[TankGirl]

Not snobbish at all! This discussion is the reason we are here (at least speaking for myself).

I think it was a thread on the Krib, or aquaticplantsdigest, I'll have to rack my brain. It is possible, certainly that it was discounted later in the thread, or I am not recalling correctly.

The thing I DO remember now about alkalinity is that phosphate (among other things) in tap water interfere with the ability for test kits to measure alkalinity (alkalinity is perhaps a better term than KH, if I may split a hair or two) so if the plants suck up the phosphate then that could explain the difference?? Is this correct thinking?

 

[tiptoptank]

I think it was the co2. Either way, I have added 1/2 cup of Crushed coral to my fluval and it is bring the kh to about 6 or 7. Which has also made my plants start pearling like crazy.

 

[jsoong]

Thanks TG!

What you said makes sense. CO2 will not decrease KH per se, but the CO2 causes the plants to grow like crazy & absorb phosphate (& nitrates too), and in that way drop the KH.

My physiology courses were almost exclusively animals, so I kept forgeting that plants do strange things!

 

[TankGirl]

jsoong - I like that theory, and I'll try to tuck this bit of info in an accessible part of my brain (do I have that? :? ) for later - this comes up from time to time.

Tiptop - CC is an excellent way to handle this, and many planted tank keepers keep it in their filters.

 

[travis simonson]

TG - I believe it was Chuck Gadd who mentioned that any sort of phosphate buffering in the water column will totally ruin the ability to properly measure the pH/KH/CO2 relationship. Things like pH-Up/pH-Down, Discus buffers, or just plain high levels of phosphate in the tap water. Hope this helps

 

[jsoong]

Yes, any kind of buffer (except for HCO3) in the water will mess up those CO2 calculators based on KH & pH.

To estimate CO2, you actually need the HCO3 & pH values. KH test will measure HCO3, but also phosphates, nitrates .... & a host of other buffers. That's why TG insisted on that test being called total alkalinity & not KH!

 

[TankGirl]

That's probably where I saw it first, Travis, as his pages are a staple in my bookmark folder, to be sure. It is also discussed from time to time in Aquatic-Plants Digest and on the Krib.

I think people don't want to get "alkalinity" and "alkaline" confused, so they use KH, but I'm trying to train myself away from this - though it is a hard habit to break. I think too we should get away from using "degrees" and stick with "ppm" but that's for another day

 

[jsoong]

But it is soooo much easier to type KH than "total alkalinity"! Actually, a better term might be "Total Buffering Capacity" .... but I've never seen that used anywhere.

I also think that we should get away from degree (dKH) - we don't use that in Canada at all! My test kit is actually in mg/l (which is ppm) and meq/l (milli-equivalent per liter). <I have to use conversion tables to convert my results to US units.>

 

[TankGirl]

Right - meq/l is very acceptable, and will be commonplace here before too long, so don't bother converting - I read plenty of posts referring to ppm alone and we all just need to face the music and retrain our brains, so you can be a part of the process of adopting a universal system. TBC!

 

[BeerBotia]

Thank goodness for palm pilots and conversion programs!

 

[Steve Hampton]

So first off I have really hard tap water. kh of about 10. But the second I add it to my tank It goes to about 3 or sometimes 2. Now I have a presurised c02 and was wondering if the co2 acually removes the carbonates

The short answer is no, CO2 does not remove carbonate/bicarbonate. We depend on this unique relationship of CO2 and carbonate based buffers to determine the amount of CO2 dissolved in water. An exact known quantity of carbonic acid forms when CO2 is dissolved in water. Carbonic acid lowers pH. The amount of the drop in pH while the KH remains stable is what allows us to determine CO2 levels. Once CO2 injection is removed the pH will rise again while the KH remains unchanged until the amount of CO2 is roughly equal to atmospheric equilibrium. CO2 moves freely into and out of solution while leaving the "KH" unchanged.

TG, I'm not sure, in this case, we could associate the loss of KH with that of lowered phosphate levels. His beginning KH was approximately 180 ppm...the drop was to 40-50 ppm...this would equate to a beginning phosphate level of (180-50) 130 ppm of phosphate...can you imagine the algae problems in a tank with 130 ppm of phosphate? Even under ideal conditions with a huge plant mass it would take quite a few months to chew threw that much phosphate.

My best guess would be that another acid is present and causing two problems. The first is a test kit interference. The second is to actually consume the buffer in the change water.

To get to the root cause of a problem like this requires a step by step process of elimination diagnosis. Could you describe all the hardscape (rocks, driftwood, substrate, etc.) in your tank in as much detail as possible including where you got the materials? And, is you source water from a well or is it a municipal water utility? Thanks for the additional information. While I know this may seem troubling to you, the solution once the cause is determined should be quite simple...and we all will gain experience and knowledge as we figure out the problem together.

And lastly, what is the pH and KH of your water directly out of the tap, and then that same water left out for 24 hours...not put in your tank just left in a bowl?