KH/pH and CO2 questions

[thartley]

Hi,

I just tested the KH and pH of my tank and I'm trying to understand now what this means when it comes to adding CO2. I haven't started the CO2 yet. I wanted to get a baseline reading on things before I started.

I'm using an Aquarium Pharmaceuticals test where you add drops one at a time until the water changes from blue to yellow. I got 3 drops in when this happened. According to the chart that came with the test, this indicates a value of 3 for German degrees dKH or a value of 53.7 ppm KH.

My pH is 7.0 with a test kit that measures in increments of 0.2 units.

Okay, so I go to the charts found elsewhere on the internet and I find that right now I have about 9 ppm CO2 with just the plants and a few fish. I should note that the tank is in the middle of cycling right now, and my ammonia level is about 0.1 and the nitrite level is less than 0.1.

If I do DIY CO2 and just use a bell diffuser (I realize a bell is an inefficient method, but I have a low light situation so I don't think it matters if I don't all the CO2 dissolved), am I going to have to worry much about pH crashes, given a dKH of 3? In other words, how much buffering capacity is 3 dKH when the pH is 7.0?

Will the dKH change any once the tank has cycled?

Thanks

 

[malkore]

3 dKH is the bare minimum for safe CO2 injection.
How low is 'low light'? If you're not over 1.5wpg, I wouldn't bother with CO2 at all. That's kind of what it sounds like too, since 9ppm is a little on the high side. Usually it's no more than 5ppm in a non-injected tank.

KH is your measure of buffering, regardless of pH.

If you do normal weekly water changes, the dKH should stay consistent with your tap water, which is/should be 3dKH also.

If tanks aren't given water changes, the KH will drop over time as organic acids form and eat up the KH. We're talking months tho, not days or a couple weeks.

 

[julicat]

"3 dKH is the bare minimum for safe CO2 injection."
-what is the danger? Drops in pH (this certainly didn't happen to my tank when I introduced my half-arsed C02 process)? Is there an outlining of the dangers that can occur when messing about with C02 introduction?

Thnxthnxthnx

 

[waffleman]

You could easily raise KH by adding baking soda, 1 tsp per 20G will increase KH by a small amount. You should keep monitoring. That is something I've been doing in different tanks.

You may notice that the PH will go up slightly, due to the increased buffering capacity.

I found the most effective method for diffusion to be a wooden airstone (creates the smallest bubbles) placed below the filter intake ( increases contact time).

If you use like a biowheel , throw it out! It actually counter acts the CO2.

m2c
Waffleman

 

[medge00]

3 dkh is the minimum for co2 because the ph tends to swing a lot....I don't recall which way it works but I think it goes down and up too much depending on when the plants use most of the co2. ph swings are pretty bad for fish.

 

[djlen3]

kH (carbonate hardness) is very important to buffer your water when injecting CO2 because, over-injecting with low kH can actually cause the pH to drop dangerously ('crash') and can kill fish quickly.
We had a member on another forum lose an entire tank of fish for exactly this reason. Very sad.
Having a larger(30 - 50gals.) tank and DIY, lessens the likelihood of this happening, simply because DIY, especially with the diffuser you are using, will not be very efficient, but the guy that lost the fish had a relatively large tank.
Be sure before injecting, that your kH can handle the gas, and protect the fish.
Test your kH again. The numbers you report don't make sense. CO2 in a non-injected tank should, as mentioned above, not be over 2 - 4ppm.
Test like this for more accuracy:
Fill the vial with 10mls, instead of the instructed 5. Then when you add the solution, count each drop as 1/2 a degree.
In other words 5 drops will give you a kH of 2.5°H.......6 drops = 3°H, etc.
If you're still reading 3°kH, you should buffer up the water with baking soda or crushed coral before injecting.

Len