Here is a picture of the C-Iso culture today. I just split the dark culture into two new cultures this morning. Following my standard phyto protocol, I took 1200 ml of used tank water, plus 300 ml of fresh RO water, in each media jar, plugged the tops with a foam stopper, and microwaved two such media jars in an 1100 watt microwave for 25:80 (Just pushed the keys from the top down the middle column on the keypad, = 26:20). This amount of time brings the temp up to about 200 F. It really just needs to get over 185 F, but I like to be certain I've killed everything. I let it cool to room temperature, and then add roughly 0.75 ml of FAF Micro Algae Grow, which approximates F/2 strength medium. I then remove the stopper from a fresh media jar, remove the stopper and airline from an existing culture that is dark chocolate brown, and quickly pour about 500 ml from the dark culture into the fresh media. I then take a prepared clean stopper and airline (either entirely new, or else a used airline I have swabbed with two alcohol swabs, in other words, swabbed it twice), and quickly place the clean stopper and airline into the new jar.
I was able to continuously culture T-Iso for appx. one year, and have continuously cultured C-Iso for almost 10 months now, with this method. I usually split the culture as soon as it gets a dark chocolate brown color, which usually takes around 10 days. Lately, I've been lazy, and have not needed as much Iso, and so, sometimes I let a culture go as long as 21-28 days before I split it (!). I guess I've been lucky. If I let the cultures go for too long, they (1) turn a funny orange color, instead of the golden yellow to dark chocolate brown, and then (2) crash, with most of the cells settling out, and the remainder of the culture turning a funny pinkish orange color.
I believe that the key to my success is the use of a microwave to sterilize my media and jars. The foam stoppers do a good job of sealing the mouth and around the airline, but do allow the air to escape, which may also help vs. a simple hole drilled in a soda bottle cap. I do currently have a good air filter on my air source, but didn't with my earlier station, and still had good success.