PH problem in angle tank,help!

[kuatto]

Got a call from an office with a fresh water tank.They are having problems with ph being high,fish are looking stressed and the plants are turning yellow(I haven't seen the tank).They are using one of those blue kits to test the water but need to lower the ph(she didn't say what the levels are). What should she use to lower the ph(if that is the problem)
I will get her to give me the levels and the brand name of the kit when she goes back to the office.

[Matt]

Yellowing plants is usually nutrients not PH. High PH is often related to high KH, and that can make it hard to lower. Likely source water issues or over-buffered (by adding baking soda to adjust PH?). Peat pads in a filter can adjust PH downward, PH-Down is an acid-based product, will work, but also reduces buffering and can cause swings. High PH will increase the toxicity of ammonia... If fish are distressing, likely ammonia or ntirites are also high. Is tank cycled?

Matthew