I don't have a secchi, haven't found any I liked. I'm looking for a decent quality plastic one. Is yours like that? If so, where did you get it from?
This is interesting about the low light thing. I may try this on my Porphyridium culture because one of them is a deep tomato red, but I have no use for it for like the next week or so and don't want to have it decline on me.
If anyone else in here grows Porphyridium, does it grow stupid fast for you as well or have I just stumbled onto luck with mine? I can grow a full gallon in just 4 days that is super red and thick with tons of it sticking to the glass ready to seed the next batch. I find this interesting as the place I bought it from states it's a slow grower.