Confusion over ph/kh/co2...

[zarkre]

I read Chuck Gadd's article that suggests one can never alter KH unless you add or remove carbonate and likewise you can only alter CO2 levels through addition or reduction.

I kinda agree with the latter but then again wouldn't adding carbonates sort of increase CO2 levels if the plants obtain carbon through biogenic decalcification?

With regards to altering of KH,i'm not too sure about this,but wouldn't the increased bubbling of CO2 further drag down the ph and in turn the kh or is there no direct relationship between ph and kh?if there isn't..then why would the addition of carbonates increase kh and in turn ph?

Besides,if i wish to have a buffer to minimise my ph swing,should i use crushed corals as one of my filter medium? Correct me if i am wrong,normally you get the desired kh first,after which you move on to adjusting your ph by introducing supplementary CO2,this should allow you to arrive at a stipulated CO2 concentration(ppm) rite? The problem comes now,supposing i want to decrease the ph so i increase my CO2 output, this process would further acidify my water and in turn gradually dissolve my crushed corals filter medium.Ultimately this would increase my kh from the release of carbonates which logically results in an increase in ph.So in the end i do not attain my objective of lowering my ph?

I'm really not too sure about all this,i had to find out because i intend to increase the kh of my current 2ft tank.(2 mth old)I just tested my kh and got a reading of 0-1dkh.(Azoo kh test) My ph stands at about 5.(tetra ph test) From these readings,i could not find out my CO2 concentration as the tables(chuck website) do not provide for ph5. My tank is currently quite heavily planted with stellata,tenellus and japonica.I have only 12 rummies in my tank. I finally decided to do some testing because my saes(hardy fish?),shrimps and otos have been perishing the next day after i put them in.My rummies on the other hand are doing pretty well,reddish noses and all...and they usually swim right above the tenellus(not at surface)so this does not suggest any deficiency in CO2 rite?

I'm really perplexed by the deaths of the above mentioned.pls do comment.

[David]

Hi Zarkre

I think you are making things very confusing for yourself. KH is the buffer that allows a certain amount of CO2 to be dissolved or expelled before a movement in PH reading.

All three are co-related unless you want a detailed understanding of this relationship, I thing you need to read a chemistry book? However since this is a hobby that is meant for your enjoyment, such details may not be needed.

The ideal range for a planted tank spans from 6.4 to 7.0...there are acceptions to this range but generally its always here. Depending on which PH level you are striving for, there is always a certain amount of KH is need to reach your PH level to obtain a rich dissolved CO2 level.

[juggler]

Zarkre:

I thought Chuck's article explained it well enough.

If you add a fix amount of Baking Soda (or Sodium Bicarbonate, which is alkaline in nature) to raise the kH, the drop in pH via CO2 injection won't alter the kH value.
However, if you use coral chips to provide for the kH, the drop in pH will cause the more acidic water to dissolve more coral. Corals contains bicarbonates that raise the kH too.

In your case, the low kH caused a huge pH swing. In his article, you can enter your pH and kH values. And I found that 5 pH and 1 dkh gives a value of 300ppm CO2. No wonder your fish can't take it. Try to raise the kH to 4. And you will notice that the pH won't drop so much.

There's another article in the Aquatic FAQ that describes the amount of Baking Soda and kH level. Check it out.

[zarkre]

In his article it was mentioned the increase in kh would be accompanied by an increase in ph,what i do not understand is doesn't this suggest a direct relationship? So why wouldn't the increase in CO2 which results in the decrease in ph bring about a drop in kh?

[theodore]

KH is affected only by the addition and removal of carbonate. That is why injecting CO2 does not decrease KH. Biogenic decalcification does reduce KH. However, not all aquatic plants does it and even if they have the ability to do it, they tend to favor C in the form of CO2 instead of CO3. Much like how plants favor NH3/NH4 over NO3 for N.

If you want KH to be more predictable, use NaHCO3. Coral chips in your filter will continuously increase your KH. Assuming that the amount of CO2 injected remains constant throughout the period, pH will increase. However, do note that our main focus is CO2 concentration, pH and KH are mere tools we use to measure it.

[sherchoo]

To put it short:

- With increase dissolved CO2, pH will drop. kH remains the same due to the presense of CO3.

[zarkre]

Thanks guys...these have somewhat cleared some confusion but supposing if i do intend to use coral chips as a buffer, how do i go about reducing my ph level when an increase in output of CO2 would ultimately lead to an increase in PH when what i wanted was otherwiser(decrease PH)?

[juggler]

Using coral chips, you can inject you CO2 in such a rate that the pH can remain constant, but the kH will continue shoot higher.
I too use coral chips, and I find it hard to get an acidic environment. Usually pH is 7, at best 6.8.
If you really want an acidic environment, I suggest you use Baking Soda instead for the kH buffer.

[zarkre]

yah i think i would try out sodium bicarbonate but would be more of a hassle compared to just having coral chips in the canister filter.

Thanks.

[confusekid]

Having coral chip would be a even bigger hassle. You would not be able to control the exact amount of CO3 in the water. As you have stated, increasing CO2 will cause more CaCO3 to dissolve, in turn push up the kH. You will not be able to get a acidic environment and you kH will be very high. Some plant and fish do not like high kH. With K2CO3 or Na2CO3 you can control the exact kH!!