Help understanding KH and GH

1 teaspoon of baking soda added to 30 gallons will raise the KH by 2 German degrees of hardness. When my tanks have 'bottom of the test' pH (that is 6 or lower) then the pH comes up to about 6.2.

You can use simple math to add more or less baking soda to any size tank to get the result you want.

1 tsp.... 30 gal..... 2 dKH
1 tsp... 45 gal.... 1.3 dKH

You will have to test and see what that does to the pH. Carbonates are not the only thing that can affect the pH.

When you are making changes to the minerals in the tank go slow. A little today, wait a few days, then a little more. The fish need time to adapt.
2 dKH change in one go is safe for fairly delicate fish, but I do not do larger changes even for hardier fish.

Monitor the results to see how stable they are. In many tanks various processes remove carbonates, so the level will drop over time. You might be OK correcting this once a week.

I can only offer you my experience in this arena.

I do all of my chemistry (adjusting KH / PH and GH in a five gallon bucket for a 5 gallon tank) before I put it into the water in the aquarium. I use Seachem products exclusively for this process.

Quick important note, KH is very important when it comes to your water chemistry as it is directly related to your PH value. PH will fluctuate more with a low KH and less with a higher KH. Buffering your GH with a higher KH is desirable; however, a strong PH buffer does reduce the amount of usable carbon your plants will get from CO2 injection. I use Seachem Flourish Excel as a carbon source supplement in addition to CO2.

At start, with the water right out of the tap, my PH is at 7.6 (stays that way after letting water sit for 24 hours), KH at 20 ppm (.35 dH), and GH at 30 ppm (.5 dH).

Adjusting the GH is a simple process, 1 to 1.5 cups of water with 1/4 to 3/8 Equlibrium mixed in, then poured into the bucket. That raises my dH to 3.5 to 5.5. I adjust as necessary depending on what I am trying to keep in the tank, be it fish, shrimp, plants or something else (less for softer water, more for harder water). I like this method better than using crushed coral as I get very precise results.

KH / PH is a little more involved. First thing I do is bring the KH and PH using acid to alkaline buffer of 1.5 to 1 (for me, that's 3/16 tsp acid buffer to 1/8 tsp alkaline buffer). That drops the PH to around 6 and bumps KH up to 40 ppm (2.25 dK). From there, I walk both back up using a reversed ratio of 1 acid to 1.5 alkaline until I hit the mark I am looking for. Once complete, I have a well buffered PH value, greatly reducing PH fluctuations. This method also yields very precise results as compared to using baking soda.

If you were to do it this way, it would be better if you adjusted a small amount, say 5 gallons at a time, then slowly introducing the new water into your tank during water changes.

If you try this, always mix it up in a separate bucket rather than in the aquarium. Also, if you mix it up in water of less than 5 gallons, mix the acid and alkaline buffers independently, then pour each into your water bucket separately.

Hope this helps.

Thanks for the reply. I'm a little confused though rpadgett37 as to why you bottom out the ph first then bring it up? I looked at Seachem Alkaline and it seems it's really similar to baking soda, but baking soda would be cheaper, no?

How long does the baking soda, or any calcium bicarbonate hold up in water before I'd need to add more? I assume once stable, adding a bit each week would maintain this?

Another thought I have, would a ph controller for my co2 work better for me or would that not provide enough co2? I do have an apex system and just ordered a ph probe so I could have more precise, constant ph readings. I can use that also to control the co2, but again, not sure if that is the best route to run co2 for plants? Since my tap comes out at 7-7.2 for ph, maybe the ph controller would allow me to keep it around there? Just shooting ideas out here.

You can use simple math to add more or less baking soda to any size tank to get the result you want.

1 tsp.... 30 gal..... 2 dKH
1 tsp... 45 gal.... 1.3 dKH

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Diana, wouldn't 1tsp in 45g equal 1dKH? I'm just trying to understand the math. If 15 gallons more are in my tank which is half the 30, wouldn't that just half the dKH number completely? Meaning, my tank I could do 1.5tsp to raise 2dKH?

While I'm thinking about it Diana, the main purpose I'm trying to do this actually is for my snails. I like the trumpet snails keeping the substrate turned over and I like ramshorns all over. The fish are completely fine with my acidic water. Rather than mess with ph and kh which I keep reading you shouldn't do, would just adding more calcium to the water to increase GH allow my snails to thrive in acidic conditions?

bsantucci said:

Thanks for the reply. I'm a little confused though rpadgett37 as to why you bottom out the ph first then bring it up? I looked at Seachem Alkaline and it seems it's really similar to baking soda, but baking soda would be cheaper, no?

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First I'll say that when trying to adjust PH, you need to focus on changing the KH of the water. Wherever KH goes, PH will follow. Not the other way around. Sorry for the confusion there.

To answer your question, because my starting KH value was so low and had no buffering capacity, and since my target PH was 6.8 from 7.6, there wasn't any choice but the drop the KH down and let the PH plummet with it. Under these circumstances, the only way to get to PH 6.8 with a strong KH buffering capacity was to go down, then bring it up again. As I mentioned, I use the Seachem acid and alkaline buffers for the task, and it is a personal preference for me. Baking Soda will do fine for raising your KH, but you have to watch it. I am not sure what to use to lower the KH.

How long does the baking soda, or any calcium bicarbonate hold up in water before I'd need to add more? I assume once stable, adding a bit each week would maintain this?

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Not sure but it doesn't matter. Regular water changes will keep your KH reasonably stable provided you are doing all you need to in the aquarium.

NOTE: Your replacement water should have the same water parameters as what is in the aquarium, matched as closely as possible. If you are going to continue using baking soda or anything else, be sure to do it in the replacement bucket and not in the aquarium.

Another thought I have, would a ph controller for my co2 work better for me or would that not provide enough co2?

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CO2 is another ball of wax, and there is no such thing as a PH controller for CO2. Basically, CO2 will always want to lower KH because of some chemistry going on in the water that I understand a bit but can't explain very well. Remember that where KH goes, PH will follow. The only thing you can control here is the amount of CO2 you are infusing into the tank. Fewer bps lessen the pressure on KH, while more bps increase the pressure on KH. The higher your KH when you start introducing CO2, the more stable your PH will be.

Here's a link to a series of articles that explain water chemistry better than I can. Lots of good stuff in here.

http://www.fishbeginner.info/home/aquarium-gh-kh-ph-chemistry-what-to-know/

Hope this helps, and FY, snails and TOO MUCH Co2 don't mix. Snails do just fine with CO2 in the water. They aren't my specialty so I don't know if there are some snails more sensitive to it than others; however, I've never read anything that says CO2 is toxic to snails unless there is too much of it in the water. And finally, there is nothing wrong with adjusting your KH and PH values. Just don't do it in the aquarium with your critters. I always do mine in the replacement water prior to doing a water change.

Diana, wouldn't 1tsp in 45g equal 1dKH?

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No.
1 tsp in 60 gallons = 1 dKH.

from 30 to 45 gallons is only 50% increase over the 30 gallon tank, so it dilutes the baking soda only about 2/3.

These numbers are only a close approximation. Tanks vary in their actual capacity, first because they are almost never what the label says, and second because substrate and other things subtract, and a canister filter or sump will add volume.

I suggest you add about 1/2 to 2/3 of the amount you think you need and measure the results.

Do not bother the GH. GH of 6 degrees is just fine.

Buffering your GH with a higher KH is desirable;

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Huh? GH measures calcium and magnesium.
KH measures carbonates.
Not the same thing, nor does one buffer the other.

KH and pH are linked. Carbonates and bicarbonates buffer the pH. Yes, CO2 is in this equation, too. Raise the KH and the pH will usually rise. Not always. Other things in the water can also affect the pH. But these don't register on the GH test.

GH is the ppm of calcium and magnesium in the water. KH is the ppm of carbonate in the water. If you add calcium carbonate you are increasing both GH and KH, but if you add sodium bicarbonate you are only raising KH. Neither GH nor KH need to be controlled to a specific value. Since plants need calcium and magnesium you need enough calcium and enough magnesium, so many people dose GH builder, which contains both, to be sure they have enough of both. Degrees (actually German degrees) of hardness can be estimated accurately enough by just dividing ppm by 20, or you can convert degrees to ppm accurately enough by multiplying degrees by 20. (You can easily do that in your head).

The pH of the water depends on the KH and the ppm of CO2 dissolved in the water. A small part of that CO2 will become carbonic acid in the water, which is what makes the pH drop when you dissolve CO2 in the water. KH does not buffer the water against pH changes. All it does is raise the pH higher than it would be if there were no carbonates in the water. But, even with near zero KH, CO2 can only lower the pH to around 5 or 5.5, because there is a limit to how much CO2 will convert to carbonic acid in the water.

KH does not buffer the water against pH changes

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For my own knowledge, as I understand it, buffering is the KH ability to minimize, not stop, PH fluctuations by absorbing acids introduced into the aquarium. The higher the KH, the less the fluctuation. Didn't mean to suggest it stops PH movement altogether.

Skipping the chemistry involved, it is enough for me to know that the higher the KH, the more stable the PH whether CO2 is involved or not. For me, it becomes important to pinpoint as close as possible the KH and PH at a specific values for the starting point. Allowing the PH to swing dramatically with the introduction of CO2 into the water due to a low KH starting point is bad for everything in the aquarium.

The first time I used CO2 in my aquarium without doing anything with the water chemistry I had out of the tap (KH start 20 ppm, PH 7.6), KH dropped to between 0 - 5 ppm and PH plummeted to 5.5 - 6. After that, I have used the buffers to set a PH value starting point of around 6.8 and a KH starting point of 100 ppm (5.6 dK). Ever since, the PH fluctuations in a CO2 environment have been very small.

Not trying to start an argument here. If I am wrong, please feel free to correct me. This is a learning game after all

rpadgett37 said:

For my own knowledge, as I understand it, buffering is the KH ability to minimize, not stop, PH fluctuations by absorbing acids introduced into the aquarium. The higher the KH, the less the fluctuation. Didn't mean to suggest it stops PH movement altogether.

Skipping the chemistry involved, it is enough for me to know that the higher the KH, the more stable the PH whether CO2 is involved or not. For me, it becomes important to pinpoint as close as possible the KH and PH at a specific values for the starting point. Allowing the PH to swing dramatically with the introduction of CO2 into the water due to a low KH starting point is bad for everything in the aquarium.

The first time I used CO2 in my aquarium without doing anything with the water chemistry I had out of the tap (KH start 20 ppm, PH 7.6), KH dropped to between 0 - 5 ppm and PH plummeted to 5.5 - 6. After that, I have used the buffers to set a PH value starting point of around 6.8 and a KH starting point of 100 ppm (5.6 dK). Ever since, the PH fluctuations in a CO2 environment have been very small.

Not trying to start an argument here. If I am wrong, please feel free to correct me. This is a learning game after all

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The only way that CO2 can reduce KH would be for CO2 to eliminate some carbonate ions in the water. I don't see any way it can do that, and I have never seen KH drop with addition of CO2. KH and ppm of CO2 are independent variables.

The equation that describes the effect of KH and ppm of CO2 on pH shows that high KH has no effect on the change in pH with the addition of CO2. The only effect increased KH has is to raise the pH, when the ppm of dissolved CO2 is constant. "Buffering" means maintaining the same pH with changes in the amount of dissolved CO2, so KH cannot be a buffer. Buffers are mixes of acids and bases, not just a base itself.

I am not a chemist, so my "expertise" in this subject is very limited, but I'm pretty sure I'm correct about this, having studied and experimented with this a lot.

Appreciate all the responses here. Lots of useful info for this to a newbie trying to understand this all.

For reference to my situation, KH hasn't changed from the faucet to the tank, even with co2. Mine is just low, sitting at 2-3. My ph swing while running co2 is from neutral (7) to about 6.4 as I measured last night. So I'm not dropping even a full point. All fish are healthy and spawning consistently (apistos, peacock gudgeons, corys).

Plants are growing well-ish. I'm still learning EI currently and how adding and removing from my mixes will affect plants. I do have some leaf melting right now, but it's def from the ferts and not from this KH issue.

I decided against adding any thing to my water to raise KH. It just isn't worth it to me to deal with water fluctuations when everything is stable just to be able to keep snails in the tank.