Undesirable algaes are all too easy to cultivate and without large numbers of snails to graze it away my tank would swiftly be overgrown with hair and slime algae. The problem is that as fresh macro-algae dies it dumps it minerals and nutrients into the water which is exactly what nuisance algae needs to thrive. The skimmer can only remove the organic waste and then only as its dissolves to a waterborne form.
Desirable algaes are very tricky though. To date I've always struggled to keep them alive for more than 10 days or so. I'd collect a great rock with a nice bit of Horn Wrack on it, withion 3 or 4 days it would start to fray and darken, the skimmer would go into overdrive and within 10 days it would all be gone!
So - I upped the lighting. But the water go too warm so I got a chiller. It also occurred to me that salinity might be an issue so I've adjusted that to match local conditions. Hopefully I've satisfied all the criteria and yesterday added a few more rocks with macroalgae on them, including a small horn wrack. I'll post the results.
31.08.10 - Just spotted 3 healthy, small horn wracks growing back on previously bare rocks. Looks like the combination of cool water, bright light and correct salinity have cracked it!