Reservoir temperature and beneficial bacterias how cold is too cold?

So I've always been under the understanding that 68* was a great
place to keep your reservoir temperatures and it has worked great.

Recently on another thread someone posted some information about
keeping res temperatures at 58*, according to that Uban Grower Remo
guy.

I understand the logic of colder water holding more DO and that's a great
feature which I'd like to optimize, but at what temperature do things
really become too cold?

In particular:

1. My roots sit in my nutrients 24/7, at what temperature is growth rate
going to begin to slow?

2. Can beneficial bacterias survive in colder temperatures? In particular
hygrozyme, and great white?


I realize I might not see that significant of gains from running at 58, as
root rot is basically eliminated at 68. I'd really like to bump up my DO
though and if I can safely do so without slowing growth or killing my benies
then I'm all for it.

Thanks

**Tried looking up some facts but most places only talk about recommended
temp of 68 and not optimal temp.**

ill be watching this thread.. i use a heater set at 69

hope a pro stops by to explain..

I was always taught to set mine at 68 sometimes I leave the ice bottles in too long and it gets to 64 but never really lower than that. I always heard people say if you get lower than 60 you could shock the roots thus locking out a lot of nutes .

That's what I've heard but someone put a link to that Urban Grower
guy talking about 58*. I dunno if my chillers can get that cool but
they're at 62* now, so well see.

http://www.youtube.com/watch?v=Jxp9TL-JqVI

I'm skeptical of this guy, but figured I'd see for myself.