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Here is an interesting thing that most people may not know about tap water. When you first run the water from the tap, the pH will probably test out with a false low level. If you air out that water for a while and test the pH again, the pH will probably be much higher.

For instance, if I test the pH of my tap water right out of the faucet, it usually tests out at right around 7. If I bubble that water for a day and test the pH again, it will be up over 8. I have well water from a limestone aquifer, it is reasonable that the pH is high.

The reason for the false low pH reading right out of the faucet is due to carbon dioxide trapped and dissolved in the water. This acts as a weak acid in the water and will affect the pH reading until the carbon dioxide is outgassed from the water.

Knowing this bit of information can help sort out many issues ahead of time. When I first got into hydroponics I did not know this and was very confused about why adding my pH 7 tap water to the system was somehow causing the pH to rise above 7.

So, when you get ready to set up a system, it is a good idea to do a pH test of you tap water and then leave some to bubble overnight and then test the pH again just to have an idea what your source water is going to do in your system.

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Comment by Moses Gonzales on March 8, 2011 at 8:34am
will do.  Thanks again.
Comment by TCLynx on March 8, 2011 at 8:31am
Do the pH adjustment while it sits in the bucket, don't adjust the pH in your system anymore.
Comment by Moses Gonzales on March 8, 2011 at 8:21am

Thanks for the feedback. OK, it sounds like I need to add a little salt and some maxicrop with Iron and sit tight.  Yes, they do use Chlorine and some of the water they "occasionally" buy is treated with chloramine.  

I've been letting water I add sit in a 5 gallon bucket for two days before adding it to the system.  I think I'll filter it first and add the bubbler as well.

Comment by TCLynx on March 8, 2011 at 7:17am

eek STOP FEEDING  At the high pH ammonia is MORE TOXIC.  The high pH actually is good for the conversion of ammonia to nitrite.  Your Ammonia is way high and so is your nirite.  Some salt (like 1 ppt) can help mitigate the nitrite a little bit and make sure you have plenty of aeration for those poor fish!


However, is your tap water treated with anything?  Like chlorine or chloramine?   That is what can really inhibit cycling.


It is also possible that the repeated additions of acid causing the pH to bounce up and down has inhibited the cycling.  See the bacteria have to adjust to a new pH slowly and if you keep bouncing it, you slow them down big time.


Once your system gets cycled, the pH will come down naturally so long as there isn't too much of a buffer in the system (lime stone or shells.)  For the time being get some chelated Iron or maxicrop with iron to help the plants along while the pH is still too high.


I don't think your fridge filter will remove the minerals very well but if it's an activated carbon or charcoal filter it might help with chlorine or chloramine.  to get rid of the minerals you probably would need to go with softened water (but with old fashion softeners that would add too much salt) or an RO filter. 


If you are working with well water, I'd just say collect some in a barrel and add a bubbler and adjust the pH ahead of time to have it on hand for water top ups or changes.

Comment by Moses Gonzales on March 7, 2011 at 10:21pm

I'v been struggling to bring the PH down on my system.  My tap originally tested at 7.4 and after a few days, my water tested at 8.0.  I put some PH Down into the system, and was able to get it to 7.8 after two days, but after that,  would put some in, get it down to 7.6 to 7.4, but it always goes back to 7.8 in within 24 hours.  Then I saw this post...

So I've tried testing the water from my fridge with an integrated water filter (Pure).  I was thinking of dumping 1/3rd of my water a few times, but figured I should test it First this time.  :-)

The water straight from the fridge is testing at 7.8, so I'm pretty sure it's my tap water that's causing the problem and not the media in my system (I originally put in "Pond stones" from Home depot and thought they were the cause).  I've since swapped out over 2/3rd's of it with hydroton.

Anyhow, do you think the built in fridge filter will remove of the minerals in the water so PH down can be effective?  Some of my plants are pretty yellow, which I believe is usually a result of low Iron.  However, I know that a high PH also inhibits the plants ability to absorb Iron, so I don't really want to start supplementing until I get the PH under control.  


Info on my system:

3 X 50G barrels (Approx. 120G+ of water)

1 barrel cut in half lengthwise.  One half planted with hydroton, the other with approx 1/3 hydroton and 2/3 "pond stones"

Using Affnan's siphons for drainage 


Current readings on my system:  

PH 7.8

Ammonia between 4.0ppm and 8.0 ppm  ( I have three goldfish, but I understand high PH inhibits the conversion from Ammonia to Nitrite as well)

Nitrite 2.0 ppm

Nitrate 5.0 ppm


Any help/comments are appreciated.

Comment by TCLynx on June 4, 2010 at 7:40pm
If you are talking about water in a system that is highly aerated, don't worry the CO2 has outgassed and won't be causing a false low reading.

What I'm talking about is water right out of a tap that just came out of pipes and before that it was either down in the aquifer or in a sealed pressure vessel or water tower, that tap water is not going to be highly aerated, simply coming out of the faucet isn't quite enough aeration to outgass all the CO2.

It is the dissolved CO2 that causes the false low pH reading from tap water.

Highly aerated water should give you a fairly accurate pH reading though I think collecting it in a container and carrying it to where you do your testing is a good idea. I don't think I would want to be trying to read a pH test with a bubbler in it.
Comment by M Cosmo on June 4, 2010 at 7:22pm
How do you get an accurate reading if you have high aeration? Can you just let it rest in a test cup for a while before you test it?

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