|03-09-2013 09:00 PM|
First time I read about someone recommending 0 kH got me wondering and also experimenting. I did noticed improvement with plant growth and my conclusion so far is that plants will do better in low kH. At least the ones I have.
Further reading on how CO2 and carbonates react with water led me to believe that aqueous CO2 decreases depending on the kH with the same gas dosage.
|03-09-2013 04:42 PM|
KH has nothing, zero, nada to do with the amount of CO2 in a sample or even the amount of bicarbonate/carbonate in a sample.
1.4825 mmol/L of NaHCO3, NaOH, KOH, etc all are 4.00 deg KH
0.71423 mmol/L of Na2CO3, CaCO3, Ca(OH)2 etc. are all 4.00 deg KH
It takes the same amount of HCl to titrate any of these to a pH of 4.5 so they all have the same KH.
Even something that is not in the carbonate buffer system like CaSO4 has a measureable KH but technically that would be considered total alkalinity.
|03-09-2013 04:44 AM|
Like yourself, I've found little support for it. I've also never heard of issues that we could verify that it was due to the KH alone and not just the old general CO2 problem people have regardless of the their KH.
Maybe a dozen or so folks have had 0 KH range water or used RO/DI post systems. KH is not absolute zero, but conductivity readings in the 3-15 uS ranges is pretty pure water.
The form the CO2 is in, is CO2[aq] mostly when we add /enrich with CO2 gas....... regardless of KH. The ratio is roughly 1:400 for H2CO3:CO2. HCO3 plays soem role, but I'll eat ghost pepper if someone wants to try and claim they can soften the KH with CO2.
I think folks trip over this when they are thinking about equilibrium systems where they are not adding CO2 gas. This is likely the source of the mix up, that and misunderstanding about how much of the CO2 is in the form H2CO3(not much).
Since only 0.25% changes to H2CO3, there's virtually no measurable effect on KH when we add CO2. Any hobbyists can measure their KH before and after adding CO2 to prove this to themselves.
Did your KH change? Nope.
If you added a stronger acid, say acetic acid, then this will attack the KH and remove it(liberating CO2 in the process and reducing the KH), or HCL etc. CO2 is not going to do much at all, in reality a tiny bit does occur, then only a tiny bit.
Measuring pH is tough without any alkalinity however.
But if you add the same rate of CO2, say 500mls of gas per 60mins to a 20 gallon tank, whether that aquarium has a KH of 0,2, 5, the CO2 will be pretty close to the same in all cases.
You may use this approach with DI/RO water, peat , tannins etc, and then bump the KH up to get your measurements, then remove the KH with water changes etc.
I use to do that to try and measure CO2 when I use dpeat and have a lot of wood I suspected of depressing pH and altering KH measurement.
|03-09-2013 02:24 AM|
In low KH water, the CO2 is more in a form like H2CO3. In higher KH the CO2 is in a form like HCO3-. Both of these can be used by plants as a source of C.
|03-07-2013 06:18 PM|
it has been a while since we talked about the KH. after doing many experiments it is clear that 0 Kh have no ill effect on anything, i still dont understand why people are afraid of
|04-18-2012 11:41 PM|
|04-18-2012 11:31 PM|
I have pretty low KH(16-22ppm range over the year), I think alkalinity would be better or split it into carbonate and non carbonate alkalinity. Seems that all plants do exceptionally well in KH's of 3-4 degrees or less. Most, perhaps 90-95% do exceptionally well at KH's 3-4 to per 15. Perhaps the alkalinity regardless of pH when using CO2 interferes with uptake of some nutrients, metals who knows...........but for most plants, it's more a functioning of CO2 uptake.
So when we add CO2, regardless of the higher KH's, the plants have ample CO2. So seem to take this as a pH preference, but it might be best to just think CO2/enrichment since so many hobbyists add the gas.
I've lived in places where my GH and KH have been from 1 degree of KH/Gh maybe 2..............to Santa Barbara/Goleta, where the KH was 11 and the Gh was 25, to Marin County where the KH was 5.5 GH 9, Davis Ca, where the KH was 17 and the GH 19, but the GH had 52ppm of Mg..........foul stuff..........then Florida with a KH of 3 and a KH of 5, to SF where the KH is 1 and the GH is about 2, same as the American River water source I have now. The Sf bay area has a very wide range of GH and KH values, East Bay MUD has KH of 2 and PO4 around 0.5ppm, Marin had a PO4 of about 1.2ppm, SF, none really.
If you live in these places for a few years and keep a variety of plants.......you get a feel for what works, what does not, but this does not begin to explain what is going on with the plants. Maybe the issue was me?
Maybe I could not grow some plants due to some horticulture issue rather than the plant actually preferring a certain KH?
Could be. I cannot ever be 100% certain. However, if I falsify that hypothesis and grow say really nice Rotala macrandra in KH of 12 tap water...........and keep doing it easily for 1 year, my hypothesis is a cooked goose, I have to reject it and accept the alternative that something other than a KH 12 is causing folks more issues in the aquarium.
Then I can be certain that a KH of 12 is NOT the issue, and it is something else. It's the something else that gets folks.
Testing CO2 can be tricky as well.
A good pH meter and flat tip probe are good items to have.
We tired a no# of tricks such as 100% water changes and leaving the CO2 needle value set at the same rate, then added 1 degree of KH with baking soda, then measured the CO2 a day or two later.
The assumption was the pH/KH relationship will hold if we have a reference KH solution without any non carbonate alkalinity or tannins. Yea, some will leach that day or two....but we assume it to be non significant. I did some comparisons with an oxyguard CO2 meter in flask, and it worked pretty good against a reference.
In the behemoth 1600 gallon tank, it also matched to inside about 1ppm of CO2 at 40ppm. Not bad for most.
Still, I would look for ideal nice thick plant health/growth......then go about seeing what ppm it is with good methods. Do not assume that any specific range/ppm (like 30ppm) is suited/optimal or Best for all aquariums.
I'm afraid using the plants as the test, then using test kits/methods/meters to corroborate or to get close...........is the better approach. I and many others have hit our heads against a wall thinking that we have enough cO2, only to realize we did not. Sounds like a broken record, believe me, I know, and I've eaten crow/my own advice in the past to accept. Finding why one tank does well and another does not is not easy, sometimes you get lucky, but if you have fish, this is more troublesome.
Findign the source of the CO2 related issue can be a game of "Who Dunnit". I had a cracked 2" long FPT 1/8" right at the thread from torquing the sucker too hard and I had no issues growing the same plant in another tank with all the same ferts/light/soil/water changes filtration etc. I knew it was CO2 but could not find it. Finally, took the entire regulator and every part from start to end, and yes.....the last thing I found...........was that small crack.
Pissed me off.
Still, I'm not sure why the plants respond to KH different, but if you have low KH, be happy. I've not seen any reason to add baking soda........at least for the plants. It did seem easier to target good CO2 ranges in the past, but this is just opinion. I would not argue for or against it.
|04-18-2012 09:13 PM|
Very surprised the answer option of "no idea, never bothered" wasn't offered.
I suppose using a calibrated fluid in the drop checker is cheating?
I'm trucking along nicely without it. :P
Hugs all around, anyhow!
|04-18-2012 09:08 PM|
My tank water which I add air to at night starts at 6.8 ph and during the day while injecting co2 goes down to about 5.4-5.5. The fish I've had never seem to be bothered at all from this large of a ph shift, and this is over years, not just weeks or months.
Some of the people whom I respect greatly for their ability to grow harder sp. plants have used RO water with no kh added back or have extremely low kh straight from their tap.
|04-18-2012 07:17 PM|
Its right out of the tap. However, it must also be noted my water is slightly cooler than the average. Around 68-65 which means it can hold slightly more dissolved gasses than the normal room temeperture. So with that combined, I think it draws down my pH a little more.
|04-18-2012 06:58 PM|
|04-18-2012 03:40 PM|
|04-18-2012 02:49 PM|
|cradleoffilthfan||I never thought I would get a chemistry lesson at a fish forum lol. I never knew what the ph of carbonic acid was at normal atmospheric conditions......My kh is like 7 or 8 and I never had problems growing aquatic plants.....co2 was still effective, you would just need more of it. Also, aren't ph swings highly likely without any buffers? I never ever ever would use 100% RO/DI water. There are no buffers at all, nothing to keep the ph stable, that's why they sell buffers to add back to RO water to reconstitute it. I would at least keep the kh at 3 or 4 degrees. 0 kh sounds crazy to me.|
|04-18-2012 01:08 PM|
|04-18-2012 05:27 AM|
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