Help With Dropping pH

[Steven M]

Hello all, I am hoping someone can help me troubleshoot the problem I’m having with dropping pH.  The weird thing about this is it seems to be happening without anything being added to the system. 

My system is comprised of an IBC fish tank with the top cut off and flipped serving as the grow bed, supplemented by a 55gal barrel split in half with hydroton media. 

A few weeks back I just finished plumbing the system, washed the hydroton and filled the tank using LA city tap (unfiltered).  I let the system run uninterrupted for about two weeks filling and draining the beds beautifully without a hitch.  The water was crystal clear.  When I went to measure the pH after week of running, it was LOW off the charts!  I tested the water directly out of the tap which measured at a 7.8 which seemed normal.  I could not figure out what could have dropped the PH so drastically.      

To be sure I took some of the hydroton clay pellets and let them sit in a glass of tap water over night.   I measured the PH and found it was still 7.8 meaning it is pH nutral.

Frustrated I completely emptied the system and filled it again, this time using a chlorine/chloramines filter.   I measure the pH from the tank upon filling to be 7.8 on 11/11/12.  Today on 11/14/12, I measured the pH to be 6.6!  The same trend of dropping pH is continuing and I have not added anything to the system other than filtered water.  I have three 300W heaters keeping the water temp at around 71F. 

Does anyone have any possible idea as to what might be causing this drop in pH or experienced something similar? Any help would be much appreciated.   

[Growzay]

Steven what kind of tester are you using?  Are you using the API fresh water master testing kit? Which of the PH testers are you using- the regular PH testing solution? Or the High range PH test solution? I assume you're using both to get both of those readings. Either way, a 6.6 PH reading is nothing to worry about. Make sure you are using the correct amount of drops of solution to the vial and the correct level of water to be tested.

[matthew ferrell]

Did you put a nitrogen source in it to help cycle?

[Rob Nash]

its a little early in the game, but a system with inert media will "go acidic" after it is mature.

i have to guess this means your water has very little hardness and thus very little "buffer" to maintain the ph... are you using a water softener?

most folks will add calcium carb and potassium bicarb etc..  i like to add 30%- 40% pea gravel or river rock. ...i havent adjusted my ph in over 2 years.

 

[Steven M]

Thank you for your replies. 

I am using the API test kit and have been following the instructions accordingly.

I have not added a nitrogen source yet.  I waned to ensure my pH was stable before doing so.  I plan to add Ace 10% Ammonia Hydroxide.  Can it be confirmed that that is a good source?

I am not using a water softener.  I haven't begun cycling yet; is it possible that a lack of buffer due to lack of hardness would case a pH drop?  Would  it make sense to add calcium carbonate or potassium bicarbonate prior to cycling?  If so, what what concentration?  My tank holds 175gal.

Thanks again!

[Alex Veidel]

I can vouch for Ace Hardware's 10% ammonia hydroxide solution. That's what I used for my system, just don't hold it up to your nose and breathe in deeply. Strong smelling stuff! You can probably go ahead and start cycling, I didn't worry about my pH too much when I did. That's the beauty of fishless cycling, no stress! You've got plenty of time to worry about pH adjusting while your system is cycling.

[Steven M]

After my pH plummeted below detectable levels I did some looking into what was previously stored in my IBC. I found out it was dipotassium phosphate which is highly acidic and might explain the situation.  I thoroughly rinsed out the container multiple times before filling using only water.  I didn't use any soap fearing the residue might impact the systems chemistry.  I'm beginning to second guess this decision.  Does anyone have a recommendation as far as using soap vs not using soap to clear the previous material from an IBC?  Or What U can use to neutralize the container before filling again?

Thanks 

[Roger]

You don't want the pH to drop too far below 6 or the bacteria that form to cycle your system won't manifest.  The bacteria prefer a more alkaline reading.  Although 6.6 isn't anything to worry about.  I wish you well.
Alex Veidel said:

I can vouch for Ace Hardware's 10% ammonia hydroxide solution. That's what I used for my system, just don't hold it up to your nose and breathe in deeply. Strong smelling stuff! You can probably go ahead and start cycling, I didn't worry about my pH too much when I did. That's the beauty of fishless cycling, no stress! You've got plenty of time to worry about pH adjusting while your system is cycling.

[Steven M]

Thanks Roger.  The problem is my pH is well below 6 and below 4 when tested with a different test kit.  I cant even get to the point to begin cycling because I cant maintain a stable pH.

[Vlad Jovanovic]

Steven, you can add a base (like potassium bicarb...or if you know how to be carefull and not overdo things some potassium hydroxide [KOH]) until the acid becomes neutralized and quits being able to lower your pH.

Make 'small' additions of some base...run your pump and re-check the pH after 3 or 4 hours. When you add the base, at first you'll get a higher pH reading, but then after a couple of hours when the acid neutralizes the base, the pH will be back down...Keep doing this till the pH doesn't bounce back down.

This is the same process people who treat their "hard" high pH top up water with acid go through (in order to pre- treat the top up water to obtain a lower pH), only in reverse...you'll be neutralizing an acid by using a base, whereas they are neutralizing a base by using an acid. Same darn thing, just 'backwards'. No biggie...

Besides, once the di-potassium phosphate disassociates (by the acid/base reaction) you'll be ahead of the curve as far as some plants essential elements go . You can look at this as a 'gift' from the cosmos as long as you just neutralize that acid with some alkalinity...