Tom Barr...question re: "KH is OK, but PH is waaaayyyy low...help?!?"

[29gallonsteve]

I have racked my brain...hard...

For the sake of simplicity...I tested my tap water...same KH!!!!

I tested pH of tap water and tank with 2 kits tap tested 7.2, tank tested 6.2????? Can't be the kit.

I tested the KH test by adding baking soda to the sample...it tracked correctly, so it is not the test...

Heres the issue, how can my fish survive (13 of them) with a CO2 level of 66-95ppm (per the table)?

Is it possible that there is such a concentration of O2 in the water (from photosynthesis) that the CO2 levels are not affecting the fish???

Thanks,
Steve

 

[Faramir]

I think there're some organic acids from peat or bogwood or something here. The chart assumes that the only buffer is (bi)carbonate, and the only acid is CO2.

 

[29gallonsteve]

I know there is no bogwood/peat in this tank. It has been up and running for 9 months. The first time the pH got screwy is when I jacked up the CO2 and cut the surface agitation.

Thanks,
Steve

 

[RTR]

With the KH and pH confirmations, I agree w/Faramir. The computed level of CO2 would sedate the fish at the least, so with normal behavior, some other acid is involved in the results.

 

[29gallonsteve]

Considering this, what, aside from wood or peat could cause the pH to drop. I have shale (in there for 9mos), sand, gravel, profile, fish waste, aquarium sealant, gravel tube, powerhead, heater, algae, live plants, eggcrate, fish would cause this?

I am not being sarcastic...could micronutrients/fertilizer/iron cause this?

Could vinyl tubing used in CO2 do this?

How about my DIY CO2?

Thanks,
Steve

 

[29gallonsteve]

Here's another thought...

I have a well stocked tank. My Nitrate levels are always around 10-20ppm (because of waste production and plant uptake).

Could the consistent production of NO3 cause the drop in pH???

I base this question on the following passage from:

http://www.automatedaquariums.com/tech2o.htm

"How much buffering does your tank need? Most aquarium buffering capacity test kits actually measure KH. The larger the KH, the more resistant to pH changes your water will be. A tank's KH should be high enough to prevent large pH swings in your tank over time. If your KH is below roughly 4.5 dH, you should pay special attention to your tank's pH (e.g, test weekly, until you get a feel for how stable the pH is). This is ESPECIALLY important if you neglect to do frequent partial water changes. In particular, the nitrogen cycle creates a tendency for an established tank's pH to decrease over time. The exact amount of pH change depends on the quantity and rate of nitrates produced, as well as the KH. If your pH drops more than roughly two tenths of a point over a month, you should consider increasing the KH or performing partial water changes more frequently. KH doesn't affect fish directly, so there is no need to match fish species to a particular KH."

Thanks,
Steve

 

[RTR]

Nitrification does burn up KH, no question there. But when it does the lowered pH and KH still correspond. Your KH is still in line with the tap figure, therefore not depleted by nitrification - or more correctly, alkalinity utilization is compensated by water changes, as it should be. So that is not the answer.

 

[29gallonsteve]

Looks like I just need to increase the KH by adding crushed coral?!?

 

[plantbrain]

1#
I think you have too much CO2 in there.
2#
You might be reading the pH a little off.
0.1pH units off and the CO2 drops by 6ppm etc. 0.2pH units around 12ppm etc.

+ or - 10ppm is a good range for most KH and pH kits.

Now, what abpout the time when you take the reading? AM or PM?
Do you run the CO2 24/7?

I have had the same CO2 reading in the past with little fish issues, but I generally back the CO2 down when I catch it. Be careful not to go too far either direction.

I doubt there's much in your tank as far as other interferring acids etc.

Regards,
Tom Barr

 

[gaul]

Along the lines of PB's last post there. As an experiment you could try taking out the CO2 for a few hours, run an airstone or something to "normalize" the tank...then test again. Theoretically, the only thing you've removed is the CO2. If the PH is still way low then something else must be lowering it.

you ought to be able to tell how much the CO2 is lowering the PH by comparing the PH with it running (in the AM, Mid-day, evening) and then with it removed.

Just my two cents.

Interesting thread, thanks!