JMAC,
I don't kow much about your water chemistry, but I had the same species kick my butt last year. Copper sulfate wouldn't do the trick alone. I then killed it using Clearigate. I guess it was all of the surfactants/penetrants in the clearigate that made the difference because the other chelated compounds didn't work either. It did come back about 6 weeks later, but I had no clearigate left. I then put copper sulfate into solution, mixed in some hydrothol 191 liquid and a good shot of surfactant. I then pounded my chest and said "Who's Your Daddy?". It worked.
I actually dropped the client for this year. It was just a plant growing machine....pithphora, hydrodyctin, etc. It was job security but I get sick of dealing with shallow, over-fertlitized retention ponds with home's associations that take 8 weeks to pay.
My advice is to keep good records and keep trying new things. As you know, what works in one pond may not in another. Going through the step-wise progression of different chemical cocktails is definitely a frustrating process.
I love Spirogyra, though. I think all I have to do is just hold the jug of Cutrine up in the air and the stuff starts to die.
Lastly, if the going gets really tough with the Lyngbya and you feel as though you've exhausted your resources (and still want to deal with it) send it off to a lab and have them perform an algal challenge. This is where the species and water chemistry are taken into consideration and subjected to mulitple tests using different chemicals/combinations at different concentrations to see what will work. Call Applied Biochemist about the test.
I feel your pain. Good luck.
