[jaybro]

As a side note to the above listed information... I have problems with slow growth of phyto in my basement due to the lower temperature (69f mostly). While the the phyto still grows, it grows slow. I wanted to stick with the separate 2l bottles rather than switching to one large culture so I would still be ok if a culture crashed and I didn't want to heat all the bottles separately.

To resolve this I took a standard 20gallon tank (I had one lying around, one of the 'long' or 'breeding' tanks would be more effective size wise) and filled it partially up with rodi water. I then place a heater in the tank to warm the tank water to the desired temperature, and my 2l bottles sit inside the tank and are warmed by the tank water. I keep phyto bottles on one side of the tank next to the light strips, and rots/bs on the nonlit side. I add a tad of bleach to the rodi tank water to prevent anything from growing in it so it stays clear. To date I've not changed the water in the warming tank, but it's not like it's tough to change a tank of sterile water in an empty tank when the time comes! (i.e. keeping the tank water clear for light transmission to the phyto bottles.) On that note, you don't have to have very much water in the tank to effectively transfer the heat to the bottles.