Hello fellow algae-nauts!
I make an effort to read all of your many emails and comments, and, whenever possible, reply; I also try to answer any questions of general interest in the FAQ or a blog post, or both.
Recently one of our kit users asked me four questions arising from posts on permaculture forums, some of which seemed to contradict things I have posted. My answers are below:
1) Reverse osmosis water will work. You have said it is mineral deficient.
You can grow algae in medium made from RO or distilled water. We give instructions on how to do so in the guidebook that comes with our kits. RO water just needs to have additional minerals added to it, in addition to what our mixes contain.
Our nutrient mix recipes assume that the medium is to be made using water containing the natural ions usually found in potable water due to contact with stone and soil. These include calcium, magnesium, and sulfate ions; algae need a some of each of these to live. If your RO filter is working correctly, the filtered water will be essentially devoid of all such ions. For this reason, if you use RO water, rain water, or any other source of particularly “soft” water (low in the above-mentioned ions), you must add a small amount of these ions to your water to use it.
Otherwise, the water you use must be dechlorinated, and otherwise free of potentially harmful contaminants. The easiest way to make water with the calcium and without the bad stuff is by filtering potable tap or well water through an activated carbon filter or equivalent. This is the approach we use for our cultures, and it’s what we recommend.
2) Temp over 92F causes cell death.. You said 35-37C (95F-98F) was optimal.
There may be strains of Spirulina that die above 92F, but ours grow best in the mid-90′s, and can survive temperatures up to about 102F. This is more typical of the strains used in commercial Spirulina cultivation. Experiment with your culture, and see what works best!
3) Harvesting can select for rod forms over spiral forms based on filtration methods.
Although we have heard much about these linear forms, we have never seen any in our cultures. They can be the result of stress in a culture, and harvesting cloths do tend to pass the linear colonies more than the spiral ones… If you have a lot of linear colonies it’s probably easiest to start over with spiral ones, there’s no easy way to get rid of them.
4) Ph over 8.6 kills all pathogenic organisms. You said over 10 ph for 24 hours. Are you just playing it on the safe side?
This is absolutely incorrect, and a dangerous thing to believe! I have worked on algae projects using waste water; any waste water engineer can tell you that pathogenic bacteria can survive for a long time at 8.6 pH. Remember that pH is a log scale, so a pH of 10 means 25x more OH- ions than a pH of 8.6! This makes a big difference. The kind of bugs that can live in your body can survive a pH of 9 for a few days, but only for hours at a pH of 10. This is not to say that high-pH water will kill cysts, spores, or any of the bacteria that are adapted to high pH (the latter, as far as anyone knows, are not pathogenic). So it is also very important to keep contaminating material – dust, cat hairs, compost tea, etc. out of your culture. So 10+ pH is not magic, but in combination with a clean, healthy culture (not too much breakage, as this can spill bacteria-promoting nutrients into the water), it should prevent any harmful organisms from multiplying. If you keep an eye on your pH, take reasonable precautions to keep your culture contamination-free, and use a microscope to watch for any non-Spirulina organisms, you should be fine, based on our experience, and that of our hundreds of AlgaeLab kit growers.