I've been reading all the discussions regarding CYA and it got me thinking about how much FC is really required. I'm not talking about what one measures with a test kit but actual free chlorine is available for disinfection. Unfortunately I hadn't been able to locate a chart that plotted ORP against FC for very low concentrations until tonight. Here it is...
http://www.aquariustech.com.au/pdfs/tec ... Disinf.pdf
Assuming that anything more than 600 mV is considering sufficient then for a pH of 7 roughly .1 ppm of FC should be acceptable. Allowing for pH up to 7.5 FC would rise to .2 ppm and for 8.0 it would be .4ppm.
First, I'm wondering if that seems correct or if I've gotten something wrong. I'm ignoring the practical issues of how one might accurately measure or reliably maintain such a value. I just want to make sure I'm interpreting the theory correctly before I post where I'm going with this.