I use a digital Milwaukee ph600. I think they are on ebay for around 20 bucks plus they come with a small pk of calibration solution. I would advise to always get extra cal solution and keep a little in the cap to keep the electrode wet.

IMO im not seeing any overfert going on in the pics. No burnt tips, etc. Im still going with over/under watering. Most likely under.

Also check out this thread. Its kinda old but it has some good info plus hes using the same soil. http://boards.cannabis.com/grow-log/...s-old-log.html