Anyone had Kh problems?

[Kiri]

I wanted to share a disaster I experienced last year which ended up with over 30 fish dying ...and me bawling my eyes out for weeks.
My fish appeared quite happy but the next morning I had ALL my fish...approx 60 up the top gasping for air. Why do these disaster's happen on work days! To cut a very long and emotional story short, it turns out that my pH was well below 6 and the cause was that my Kh was up the creek. I am now super paranoid when a fish goes to the top of the tank and immediately pull out the water test kits to calm me down.
I have had to put in 20mls of Kh booster daily to get the levels where they should be and now I'm going to put some aragonite into the tank so it keeps my Kh constant without chemicals. The guy at the lfs said that in the UK they have this problem as well. What an expensive month that was! Thankfully all 4 tanks are thriving, crystal clear water and very active, happy fish.

 

[Bol]

Sorry to hear that, Kiri.

By "up the creek", I'm guessing you mean your KH was very low, as in less than 1 degree or about 20 ppm?

If so, although the aragonite will help, from my understanding it does "wear out". I could be wrong.

Many people use just plain old sodium bicarbonate (i.e. baking soda) to increase their waters' KH. It seems like an easy and cheap method. You might want to do some research on that.

 

[guppygirly]

I was just about to ask about Kh. Mine seems to be dropping. It's at 80 right now, but it usually is around 120. I haven't added anything or done anything except a water change. Will this help?

 

[Bol]

guppygirl,

If you're asking "will adding baking soda or aragonite help to raise my KH?" then the answer is yes, it will. And, you'll get a corresponding raise in pH, too.

However, it's probably a good idea to find out why your KH is dropping, before fixing the problem. Normally, KH will stay stable (assuming you use tap water).

 

[Kiri]

What can make a KH drop? My tap water does test low for KH but I have no idea why it drops... my cold water tank has the opposite where the pH goes too high.

 

[Bol]

What can make a KH drop?

That's a very good question. One that I've never found a clear answer for.

Don't quote me on this, but this is my interpretation of the best answer I've found:

KH is carbonate hardness. It is a measure of carbonate ions (HCO3-) in your water.

There is a cycle that happens all the time in your tank that continuously breaks down carbonic acid (H2CO3) into hydrogen ions (H+ ... the concentration of which is what we call pH) and carbonate ions (HCO3- ... again, the measurement of this concentration is KH), and then turn them back into the neutral H2CO3. That is, a neutral compound breaks into two ions, then recombines, quickly and constantly.

Usually, this cycle is self-sustaining, and your KH stays stable, and to a point, so does your pH.

However, if your KH is already low, then apparently the presence of acids can upset the balance of this cycle. How exactly that happens is the part I've never learned.

It would seem that in this condition, some of the carbonic acid is not available for the above cycle, so you don't see as many carbonate ions (which means your KH drops) or hydrogen ions (which means your pH drops).

Again, my understanding of the chemistry involved is pretty shaky, and I hope I didn't make a mess of that explanation. But it basically comes down to "if your KH is already low, it can drop further (along with your pH) in the presence of acids". The acid in this case is most probably nitric acid -- the salts of nitric acids are "nitrates".

 

[Kiri]

I hated chemistry at Uni but you're explanation has helped a lot..thanks!

 

[susangc]

Bol, my water's chronically very soft (40 ppm out of the tap) but I don't have problems keeping the pH stable. My nitrates are under control but not 0. I do a 25% water change every two weeks. Why am I not having problems with pH? Are the water changes keeping me ahead of the problem?

Susan (just trying to understand )

 

[guppygirly]

What makes Kh drop? My pH hasn't changed at all just the Kh...

 

[susangc]

Good question; I picked up on the pH thing from Bol's post, but I've read it elsewhere as well.

When I first set up my little 3-gallon and started testing, I was surprised at the initial kH results -- about 120! I had written to the town water chemist AND tested the water coming out of the tap. I finally decided that the fizzy tab I used on my Amazon sword at planting time was probably the reason for the higher reading, because over time with several water changes, the kH reading has come down. (I've also switched my plant food.)

All that is fine for the fish in my tank -- they prefer soft water anyway -- but I never noticed an accompanying drop in pH, and I was just wondering why.

Susan

 

[guppygirly]

My test kit (Mardel 5in1 strips) says 120ppm is in a good range and at 80 it says to use buffer up. I don't mess with water chemistry though, I'm not qualified. I usually just do a water change...

 

[sinistral]

However, if your KH is already low, then apparently the presence of acids can upset the balance of this cycle. How exactly that happens is the part I've never learned.

It would seem that in this condition, some of the carbonic acid is not available for the above cycle, so you don't see as many carbonate ions (which means your KH drops) or hydrogen ions (which means your pH drops).

It's been a long time since General Chem for me, but as I recall Bol has hit the nail on the head. kH is one part of the total buffering capacity for the solution of water and other substances in an aquarium. Any weak acid or base can function as a buffer; that is, a solute that can keep a solution at a stable pH (for example, carbonates and bicarbonates are the primary buffers in a typical aquarium). These can effectively neutralize any incoming strong acids or bases and thus function as the primary stabilizers of pH. Each molecule of buffer, however, is used up to neutralize a molecule of the incoming acid or base.

Adding acids or bases to a solution will eventually use up the existing carbonates and bicarbonates (sooner for low kH, later for high kH). Continuing to add acids, for example, will deplete a buffer's ability to stabilize pH. Eventually, the buffer gets used up, and the new acid or base becomes the determinant of pH of the solution. This is why nitrates (nitric acid) over time will use up buffering capacity (kH) and begin to alter the pH of the aquarium downwards.

Side note: If you've ever seen a titration curve graph, you know that this explains why adding and adding and adding acid or base to a buffered solution keeps it stable...and then suddenly there's an abrupt change in pH when the buffer is used up.

This presumes that the only substance entering or leaving the solution is nitric acid. If you are doing regular water changes and have decent kH, a pH shift won't occur, as you are constantly replenishing the solution's ability to buffer against pH change, as well as removing nitric acid from the solution.

I hope that wasn't too confusing. If a real chemist wanders along and wants to correct me, I hope I wasn't too far off.

 

[guppygirly]

Thank you so much to both Bol and sinistral! This was very educational. The Kh thing has been confusing me forever. All the books say it in different and vague language.

 

[Bol]

There's one more thing to keep in mind... KH levels are expressed in two forms, parts per million and "degrees" (sometimes called German degrees).

1 degree is equal to 17.9 ppm.

Some test kits, namely Mardel strips, measure in ppm. Others, such as the AP KH kit, measure in degrees.

So, when you see "my KH is 120", it's probably ppm, while "my KH is 5" is most likely degrees.

"Nominal" values for water KH are 3 to 6 degrees (or roughly 55 to 110 ppm). However, usually a KH of up to 10 degrees, or 180 ppm, is usually consiered "safe" for most environments (some fish, of course, are a little particular).

From what I've gathered, your KH should not normally drop in the presence of acids unless it's already "very low" to start. The definition of "very low" here seems to vary. Many people consider it to be 1 degree (20 ppm), but some say it's anything less than 3 degrees (55 ppm).


(For some reason, quotes don't work for me right now)

Susan,
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Bol, my water's chronically very soft (40 ppm out of the tap) but I don't have problems keeping the pH stable. My nitrates are under control but not 0. I do a 25% water change every two weeks. Why am I not having problems with pH? Are the water changes keeping me ahead of the problem?
---------
My guess (and again, I'm doing a lot of guessing here) is that your pH is staying stable because of a combination of two things:

1) Your KH of 40 ppm may be, for this purpose, higher than "Very low".
2) Regular water changes are keeping acid levels low enough to not upset the carbonate cycle.

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I was surprised at the initial kH results -- about 120! I had written to the town water chemist AND tested the water coming out of the tap.
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So, you're saying the first test in the tank showed 120ppm, and your tap water tested 40ppm?
How long after filling the tank was the tand test taken?
What did your local water treatment plant say you should expect for tap water?
And, do you have any in-house water treatment?

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I finally decided that the fizzy tab I used on my Amazon sword at planting time was probably the reason for the higher reading, because over time with several water changes, the kH reading has come down. (I've also switched my plant food.)
----------
If the fizzy tab you mention is something like a Jungle Plant Care tab, that's basically just CO2, and I wouldn't think it would have any measureable effect on your (particular) KH. The most likely thing is it lowered your pH temporarily (introducing CO2 does that, but that's a different discussion ). If it had any effect on your KH (which I personally doubt), it would have lowered it.

guppygirly,

"What makes Kh drop?"

Frankly, I'm not sure what will make it drop from 120ppm to 80ppm. It seems that something is binding your carbonate, so that it cannot ionize normally. I'm not sure exactly what's doing that, though. Basic chemical knowledge would suggest it's an ion with a single positive charge, that results in a carbonate compound with a relatively strong bond. Not sure what that could be, though.

"My pH hasn't changed at all just the Kh... "

Well, that does seem a bit odd, but remember....

pH is a measurement of the concentration of hydrogen ions.
KH is a measurement of the concentration of carbonate ions.

While they are related (as the two ions interact with each other), there are other things that react with hydrogen ions also. That is, there are reactions which will affect your pH that have nothing to do with carbonates.

Once again, I'm pretty shaky on my chemistry, and hope I haven't spread a bunch of misinformation. But, I think that while some details are probably wrong, in general this is mostly "true".

 

[susangc]

Hi,

The average kH rating is listed by my town at about 35 ppm as CaC03, so the 120 ppm reading was a surprise. I have no additional water treatment, and nothing went into the tank that wasn't rated for aquarium use. I took the tank reading two days after setting up the tank and repeated it two days later. I wish I knew what happened, but the readings now make a lot more sense.

Susan