# Why is my KH climbing



## carsonc (May 30, 2007)

The KH started out at 11 when first tested and has been climbing ever since, I had to reduce the CO2 because of visible stress on fish (headlight tetras), PH at that time was 6.7.
I was trying to get the system stable at a PH of 6.7 so that I might someday add some Discus, It seems like I can't add any CO2 without bothering the fish and I think it is related to the high KH but chemistry is not my thing.

Tank is 75 gal 1 month old. If it ever cycled it was very slight. Comon plants from LFS with a aqua soil, peat and silica sand substrate, total depth 2 to 3 in. 2 in deeper in back corners in 2 confined areas. Lighting is 2 VHO 110 watt bulbs left over from a reef tank. Plants are growing at an unblievable rate and look healthy, The fish look fine but will stay near the surface more than they should. 5 our of 20 have died in the last week, up to that point there were no deaths.

tap water KH is 8 (salifert test)
ro water KH is .6 (salifert test)
water change water (45gal trash can) 4.8 (salifert test)
water change water is 50% tap and 50% RO with amquel added
tank water KH 14 (aquarium pharmaceuticals)
tank water KH > 16 (salifert test)

5 weeks in operation
NO2 is 0 (1st week was .25)
NO3 is 0 (2nd and 3rd week was 5)
NH3 is 0 (3rd week was .25 for 5 days)
PH is 6.9
KH is 14 or > 16 (different test kits)

pressurized co2 with controller set for 7.1 - 6.9

Can anyone see what I have done wrong ?
Thanks Carson


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## BryceM (Nov 6, 2005)

I think you've got a handle on the chemistry behind KH, pH, and CO2, but let me just go through it anyway. If your fish are at the surface and several have died recently you have TOO MUCH CO2 in the aquarium. 6.7 is an impressively low pH for a KH of 14. All of the fish should have been dead. The plants will love it, but the fish can only tollerate so much.

Discus prefer water with a low buffering capacity (KH). Just because you can drive the pH down to 6.7 using an acid (CO2) doesn't mean it's acceptable for discus. Once you supply water with an appropriate KH (say between 2 and 5), the pH will fall right into line. You need to find out what is adding carbonate to your water. I suspect that your silica sand might not be completely inert. It almost sounds like you've got crushed coral (calcium carbonate) or some other readily available carbonate source to cause that much of a shift in your KH.

Take some of the substrate out of the tank and test it with a strong acid such as HCl (often sold as muriatic acid for swimming pools). Be careful - don't spill the stuff. If the substrate fizzes, you've found the culprit. Some substrates (Eco Complete, Onyx) will gently buffer the water, but nothing like what you're seeing. Suspect either the substrate, KH test kit, or pH measurements. Your controller is callibrated and verified to be working correctly?


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## mikenas102 (Feb 8, 2006)

In addition to testing the substrate, do you have any rocks that you are using in the tank? You'll want to test those with the muriatic acid as well.


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## carsonc (May 30, 2007)

guaiac_boy I am the one with the pinpoint controller that you and others helped to get working. It calibrates good at 7.0 but will only calib to 4.5 on the 4.0 fluid. I don't think that calibration is the problem I think that I was just trying to get the PH down without knowing the effect of the high KH. I have set it for a PH of 8 so that it will not come on and added an air stone to try and save the rest of the fish. I think I will leave it that way until the PH stops climbing. I have no idea what is causing the high KH, I will test the sand and whatever else I can remove with the acid. 
Will a high KH kill the fish and or plants buy itself (with no CO2 being used)
Thanks for your help again
Carson


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## BryceM (Nov 6, 2005)

No, a high KH will be tollerated by _most_ fish. Some species like tetras, discus and such strongly prefer a low KH, but can _usually_ acclimate to survive at higher values. Rapid, large shifts in KH (like everything else) should be avoided since this will certainly cause stress. I'd recommend that you find a pH/KH/CO2 chart on the internet and spend some time looking at it.

The chart is full of innacuracies and problems, but it will give you a general idea about how the relationship works. Looking at the "chart", a KH of 14 and a pH of 6.7 gives an "answer" of around 90ppm CO2 if I remember correctly. This is an enormously high value and is certain to be lethal to many fish, especially if they don't have time to acclimate to such high levels. 30ppm CO2 is said to be a pretty good target value. Keep in mind that there are many, many problems and issues that surround the "chart". It is notoriously difficult to measure pH and KH accurately and even small errors result in rather large changes in the estimated CO2 concentration. The chart is also only valid if carbonic acid (from CO2) is the only acid in the aquarium - something that is simply not true.

What you should look at is the way that CO2 concentration chages as KH goes up and as pH goes down. Look at the general trends and I think it will be easy to see that a pH of 6.7 is NOT a good idea with such a high KH. A pH controller can only work properly when the KH is stable.

Regarding the pH controller - if it will not calibrate correctly between 7.00 and 4.00 I wouldn't trust it and I absolutley wouldn't trust the lives of my fish to it. Either the probe is shot or there is a problem with the internal circuitry. pH meters are finicky even when everything calibrates properly. You're dealing with something that has demonstrated that it is unable to perform its intended function. I say buy a new one or go without. There's nothing wrong with just using a bubble counter to estimate CO2 dosing.


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## carsonc (May 30, 2007)

I agree with you about the controller and it is now out of the circuit. The CO2 is shut off and I have an air stone going. I will let the tank calm down and try and find out what is causing the KH to increase. I have to wait till tomorrow to get some muratic acid to test with.
When one is using a bubble counter does it matter if it is in the base of the difuser (internal) or mounted on the CO2 bottle (external)
Thanks again for all you help
Carson


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## carsonc (May 30, 2007)

Well I got the acid and the only thing that bubbles is the sand. I did not have any that was not in the tank so I removed some and rinsed it in di water a few times. It behaves different than I would have thought, in that little balls of something come out of the sand and fizz but they move around under there own power. Almost like there is some thing else in the sand. I don"t know if came in the sand or is some reaction from being in the tank .There is no reaction with vinegar at all. The sand is pool filter sand and the bag said it was silica.
The tank has stabilized at 7.5 and KH of 12, lost 2 more fish before all the CO2 was used up.
Carson


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## BryceM (Nov 6, 2005)

Well if it fizzes at least part of it is calcium carbonate (limestone), not silica. That easily explains your problems. If you continue to inject CO2 you'll gradually deplete the CaCO3 in the sand but it can take months or even years depending on how much is there.


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## carsonc (May 30, 2007)

I think I will leave it as is for now, the tank has only been up a short time.
Maybe with a lot of water changes and a little time it will be ok.
Thanks for you help
Carson


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## hoppycalif (Apr 7, 2005)

As long as you have carbonates present in the substrate the KH will go up with time. Incidentally, you haven't said whether your KH measurement is KH as ppm or dKH, degrees of KH. There is a vast difference. I suspect you are getting ppm instead of degrees. RO water, for example, should be lower than .6 dKH, if I remember correctly. 

You noted that your NO3 reads zero, but you were injecting CO2. Plants have to have nitrates in order to grow, so the NO3 should be at least 5 ppm, preferably more. And, you also need phosphates, around 1 ppm minimum, to grow plants. Then, there are the trace elements. You need to be dosing nitrates, phosphates, preferably potassium nitrate and mono-potassium phosphate, to get potassium too. And you need to dose a micro-nutrient mix, such as CSM+B or Flourish.

Finally, rather than keep guessing about how much CO2 is in the water, just pick up a cheap Red Sea pH checker (drop checker), fill it with 4 dKH distilled water and a couple drops of pH reagent and you will know how much CO2 is in the water - the solution will be green for 25-40 ppm of CO2.


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## carsonc (May 30, 2007)

The aquarium pharmaceuticals just says KH and reads 13
The salifert says dkh and reads 14.4 
I would assume they are in the same format, ???
The R O unit is due for a filter and membrane change so it may be just showing its age.
The last aquarium I had was a reef tank, and readings of "0" were good, I guess I have not got that out of my mind yet
I have the CO2 set so that the PH is 7.3 (to go with my high KH) I made a drop checker and mixed some baking soda with DI water to get the 4 KH, I used 4 drops of ph checker so the color would be a little darker. It has been in the tank 3 days and so far has gone from blue to blue-green, so I think if this does not change in a couple of days I will increse the CO2 so that the PH is 7.2 or 7.1
The plants are growing very fast without adding any ferts, I did use peat and planteing mix under the aquatic soil, so that might explain the fast growth and the "0" readings.
Thanks 
Carson


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