The pH Story

[Joel Berg]

My API aquarium water tester and my new air pump arrived in the mail today. I immediately began testing my water to see how it compared with the test strips I had been using. To my surprise my pH level was at 8.2! What the crap?! The test strips gave me a neutral level this whole time! No wonder my sprouts have been dying off. I immediately knew I had to decrease the pH somehow. I began to think back and formulated a problem in my head. Here we go, back to general chemistry.

You have a 5 gallon aquarium with an initial pH of 8.2. You have acetic acid that is 5% concentration. The acetic acid has a K_a of 1.8*10^-5. According to Nelson's book, you want to get your pH to at most 7.0 and no less than 6.5. What volume of acetic acid do you have to add to get in this range? 

I used to vaguely know how to do this sort of problem, but I now understand I must relearn this content! What I ended up doing was taking a half gallon sample of my water and adding acetic acid slowly (2.5 mL at a time) until I got the concentration I wanted, then multiplied that amount by 10 and added it to the tank. The pH was overshot by a little bit, and I ended up getting it down to about 6.4 which is not bad. But next time I will learn how to solve this problem on my own. It just goes to show that aquaponics is not just for the people who love plants and fish, but can also be for chemistry nerds (which I am not). 

Happy Testing!

[Joel Berg]

Thanks for the advice

[Keith Rowan]

salting to 3ppt

[Joel Berg]

Okay, thank you for this, i won't do anymore adjustments. I will test for ammonia and nitrate often though. So if I do get a spike, what do you recommend?

[Keith Rowan]

don't mess with your ph.. it's good to be high when you are first cycling your system, (it was actually pretty near perfect for cycling!) and unless your media is buffering your ph, it will drop, and you will have to raise it.. if your ph drops too low, your bacteria will die, and you'll get an ammonia spike