PH problem in angle tank,help!

[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