Hello everyone. I have been keeping guppies for a few years and have always kept the lighting timer at 12h on 12h off. I was chatting with a friend today who told me he found his guppies bred quicker with 16h on and 8 off. I was told 12/12 when I bought my first guppies and I have never questioned it. I would like to know what other guppy keepers do and whether it actually makes a difference. The scientist in me feels an experiment coming on but the fish keeper thinks if something is working don't touch.