Discrepency with pH tester
 

I recently got a package of individually wrapped Mardel test strips, and when I tested my water for pH the number was showing up as lower than 5.5 each time. I was worried because I have snails in my tank, so I went to the store intending to get crushed coral to gradually bring my pH up. Luckily in this case, they didn't have any, and I ended up buying a SeaChem pH monitor instead to prepare for the steps I would take to manage my water. Surprisingly, the pH according to the monitor is much, much higher, reading 7.4.

Which one should I believe?

i am new to fish keeping but not to pH. Check the expiration date of the strips, also strips have bene known to be off by a substancial % but that sounds like a lot........suggesting something wrong with the strip wheather bad or contaminated. The meter is more reliable but all the ones i had used went thru a pretty precise calibration procedure with more then one calibration fluid. I am not sure what calibration procedure yours requires but work cleanly with the probe and care for it when not in use. Best of luck......nothing is absolute.

I did check the expiration on the strips and it was Jun 2012. The monitor is just a little plastic card with a chemical tab in the center that sticks onto the glass. I'm cheap :P It's been on there overnight and stabilized in its reading. Throughout this week I probably used 4 strips and they all read the same thing. I also did a tap water check to see if it was something in my tank causing the reading when I thought the pH was super low. I'm inclined to trust the SeaChem monitor more, but I don't know enough about different brands to make a fair judgment.

Pick up a quality liquid test, strips or other dry methods are known to be horrible at accuracy sometimes.

ditto zof