How Best to Lower pH While Raising KH

[George Monnat Jr]

Hi all. My tank is doing pretty well, it looks great and everything looks healthy. My target parameters are pH 6.8-7.0 and KH 6-8 dKH. I'm close but not close enough averaging pH 7.3 with only a KH of 4 dKH. I already run my reactor with peat moss pellets in the first chamber and GAC in the second to lower pH and remove the yellowing tanins. My ATO uses RCA DI, and when I do water changes my ATO refills the tank with that same RCA DI. I like the lower pH (around 6, I think) but that drops the KH, too. (Also GH but with Texas Holey Rock and leftover crust from the SW days, my GH has been steady around 8-10 dGH.)

I want to raise the KH while simultaneously lowering pH. That's hard to do since there's a definite relationship between the two - and CO2. It's easy to find charts and explanations, but I like this one.

From that and others I saw, it looks like my CO2 is around 7 ppm. It should be around 20-25 ppm. I guess leaving my windows open has lowered it in the house. I also guess I have more plants than animals.

I picked Anubias and Java Ferns so that I wouldn't need CO2, but I might be forced to add it.

I plan on trying to use a combination of Seachem Acid Buffer and Seachem Alkaline Buffer in the DI water to get a specific pH/KH. They're supposed to come with instructions on how to do that. I might try Seachem Equilibrium in the DI if my GH starts to drop. The GH test is tough as it's really hard to distinguish between the yellow and light green shades with the API drops.

Does anyone have experience using those, especially in a combination for RO/DI?

[Reburn]

Why do you want to keep your KH at that level? Really the only way to get your ph down is to lower your KH. That why some of the minerals to remineralise RODI water has almost no KH in it. I understand what your trying to do by lowering your PH levels to increase your CO2 PPM but I don't know of a way to accomplish it without lowering your KH.

I use salty shrimp products to remineralise my RODI water. They have a GH that has no KH in it and they also have a GH/KH that I uses in my guppy tank since they need hard water. If you want to drive your PH down the best way is to get rid of your KH and inject CO2 to drive your PH down.

[George Monnat Jr]

KH is a measure of your pH buffering capacity. Less than about 4.5 dKH and you risk big pH swings. My pH has already been flakey with me around 4 dKH. Carbonates are also needed for building calcium structures. It's critical for SW with all the coral, but fish, snails, etc. to a much lesser degree need it, too. Snails need a GH > 7 dGH to stay healthy, too.

I picked up some Seachem Acid Buffer and Seachem Alkaline Buffer at RCA today. Right on the label it says if doing water changes with DI add 2:1 Alkaline:Acid buffer to the DI for a pH of 7. I'm going to try that and see what happens.

I keep a spreadsheet of ideal parameters for livestock. Here's the critter one (I have another one for plants, but it's wider). I don't try to adhere to all of them, but I like to pick a median range as a target for each parameter.

[George Monnat Jr]

Last Friday I finally rented a 20 pound CO2 cylinder from Round Rock Welding supply, got it all hooked up, and programmed. I'm really happy with it so far. You can see that my pH is now stable within a +/- 0.5 around 7.12 pH (with the occasional quick spike to 7.20 or 7.21). The CO2 regulator needle is still on the 1000psi line, so I bet this cylinder lasts me months at a yearly rental of $63 after taxes. I haven't refilled, yet, but I think it's really cheap.

As for the programming...

[George Monnat Jr]

... [saved 1st part so I don't lose it]

As you can see, when I first set up the CO2 with a simple program, turn off when pH drops below 7.20, I got horrible dips in pH. That's because the pH changes and the probes register the change minutes after the CO2 is added.

I needed a way to limit the time the CO2 was being added (both the cylinder regulator solenoid and the pump for the cyclonic diffuser) regardless of the instantaneous pH reading. I also needed to make sure that the outlets stayed off for a minimum amount of time and didn't just turn back on since pH hadn't dropped, yet.

I surfed the web and found a couple solutions for using virtual outlets to create the maximum on time and the outline line needed for the minimum off time. I created two outlets for the CO2 solenoid and the diffusor pump and a virtual outlet for each of them. The two pairs of outlets have identical programs, so I'm just showing the one for the solenoid.

Pump1_5_3

Fallback OFF
Set ON
If pHsump < 7.15 Then OFF
If pH2dt < 7.15 Then OFF
If Outlet VOutlet3_A1 = ON Then OFF
Min Time 005:00 Then OFF

VOutlet3_A1

Fallback OFF
Set OFF
If Outlet Pump1_5_3 = ON Then ON
Defer 000:30 Then ON

I let them cycle with nothing plugged in overnight to verify my program's timing (that's why the pH really crept up). It looked good, I plugged everything in, and I've been really happy with it.

Now my KH = 9 dKH and pH = 7.12, which is where the sources say is ideal for my livestock. I guess those bodies of water have a lot of CO2 to get those parameters. If the CO2 runs out or fails off, then the pH will rise to about 7.4 or 7.5. That's ok, too, for a day or three. If it somehow fails on (program and solenoid are designed to prevent it), then I'll probably have a tank crash as the water becomes very acidic. The plants will probably be happy, though.

[Reburn]

George a word of advice. Worry less about PH. PH isn't nearly as important in FW as it is SW. Worry more about a constant co2 ppm level. If your co2 level fluctuates too much black beard algae and stag horn algae will become your best friends and the are as hard as aptaisa and dynoflagellates to get rid of.

[George Monnat Jr]

George a word of advice. Worry less about PH. PH isn't nearly as important in FW as it is SW. Worry more about a constant co2 ppm level. If your co2 level fluctuates too much black beard algae and stag horn algae will become your best friends and the are as hard as aptaisa and dynoflagellates to get rid of.

I appreciate the advice. If you see the chart in my original post, with pH 7.1 to 7.2 and KH of 9 dKH, my CO2 is 20-25 ppm. That's listed as the ideal CO2 level in FW aquariums.

There are lots of other sites that concur:

This is the proper CO2 chart to use when measuring carbonate hardness against PH to determine the proper amount of CO2 for your aquarium. I recommend 7.0 (plants and fish from both acid and alkaline regions can all coexist in 7.0 PH or neutral PH!) for the PH which as you can see by the chart that your KH or carbonate hardness can range from 2-10 KH to hit optimum levels of CO2 for your aquarium at a 7.0 PH. Also indicated are the optimum KH values between 4 KH and 8 KH.

[Reburn]

With out getting too long winded because I hate to type lol.

30ppm is ideal.

Watch your fish for signs of co2 stress. It they are stressing cut it back. It they seem fine bump it up a little.

Get a drop checker on ebay out of Hong Kong for $10. Remember that the drop checker takes hours to change colors so always always uses your fish as your high co2 reference. Be danged it that drop checker is still green.

Only mess with your bubble count once per 3 days or so. (Unless your fish are stressing then air stone in an emergency co2 removal procedure)

Throw that chart away. It's good to understand the theory of co2 ppm in relation to PH. However you are not running a tank with no driftwood, fish, substrate, plants. The chart is accurate in RODI water. It's application in a aquarium usage is sketchy at best because there are too many things that will affect your ph, driftwood, peat moss, different substrates that buffer PH, KH and the amount of doc and ferts in your water column

Lastly drive your co2 higher as your plants get bigger and cut it back a little when you trim. Remember that co2 consumption increases and decreases with plant mass.

[Reburn]

Think about this. Your peat moss will lower your ph. But your ph is lowered due to outside influences not due to co2 saturation. Your co2 hasn't changes just your ph due to the peat moss.