DI water and PH

[reavely]

I had switched to DI water 2 months ago to get rid of red slime. Checked SG and PH of mixed water at changes (8.5 PH) but oddly enough the tank PH gradually fell off from 8.2 to 7.7 over time. Then I had a green hair algae problem! It wasn;t until the LFS guy told me the DI process lowers PH that I tested the UNMIXED H2O that I TOP-OFF with daily, and came up with PH 6.4!!
NOw I have to add buffer to the fresh-top-off H2O to bring it up to 8.2 or so.
anyone ever had this problem, is the LFS guy right about DI process?
PS - finally got a digital camera -check out the "aquaria" page on my site:
http://www.unc.edu/~reavely/

 

[bang guy]

Originally posted by reavely
NOw I have to add buffer to the fresh-top-off H2O to bring it up to 8.2 or so.
That's a really really bad idea.
Your tank PH has absolutely nothing to do with your switch to DI water. Low PH is caused by excess CO2. This can be from rotting detritus, poor gas exchange, overstocking, etc.

 

[reavely]

hmm, well with no rotting detritus that I can see, and plenty of circulation, air-infusion at the protein skimmer, and exposure at the filter return, that only leaves overstocking, which I thought I was admittedly near, but still short of. I had switched to DI water because my tap water had hi phosphate levels, which fed the red slime, no? since then the red slime is gone, the green hair is in. over the last four days of buffering the top-off water though, the hair algae (and nothing else) seems to be thining.
But I'm also confused - wouldn't adding nearly a gallon of top-off water, every day, with a PH of 6.5 or so, have an affect on the PH of the tank?, particularly as that top-off water increasingly replaces the evaporated water put in at x-changes?
tanx

 

[reavely]

and Bang Guy, why is buffering the top-off water a "really REALLY bad idea?" what harm could it do?

 

[stinkyfish]

i also had a low ph in my tank after i removed the glass top and had to start doing daily topoffs w/ ro water. i too checked the ph of the ro and found it to be quite low so i started adding buffer to the 5 gal. container of ro that i use for topoffs. it seems too have solved the problem. i'm going to tag along to find out why this is really really bad.

 

[bang guy]

Di water really doesn't have a PH as it is stripped of all Ions. As atmospheric gasses quickly dissolve into the DI water the PH will fluctuate. The fact that your DI quickly drops to the low 6's tells me there's an overabundance of CO2 in your air.
Buffering your topoff means that you are probably adding more carbonate than calcium to your system and this will eventually cause an imbalance.
If you have actually tested ALK and it's low then there's no problem adding the buffer to your topoff. But not as a generally normal practice.
So, after buffering topoff, what is your ALK level now?

 

[searcher]

Wouldn't DI water have a pH of 7? (H2O stripped of all its H ions would be Oxygen). So even adding that would raise his pH a little.

 

[reavely]

ok my DKH is ~ 6.0 - a bit low.
But it should also be taken into consideratino that I've recently switched from adding calcium manually once a week, to a Kalkwasser drip - about two weeks ago. I continued adding a carbonate/bicarbonate additive manually once/week, AND have just begun adding baking soda to the top-off water (a gallon/day) within the last four days. And I'm still measuring a low DKH... what's THAT tell you?
I use an airstone in my top-off water bucket - what effect does this have?

 

[reavely]

PS my CA concentration is at ~440
PH with actinic lights on is still low, but rising at 7.8

 

[the reef]

Originally Posted by reavely
PS my CA concentration is at ~440
PH with actinic lights on is still low, but rising at 7.8
raise your dkh directly in the tank and not the make up watter