Green Cyano vs nutrient balance

punchy7080

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My tank has been setup for about six months. Established/cured live rock was used (like 10+ years old). No cycle and very brief/light ugly period of some diatoms etc. in the first couple months. Up until recently there was ZERO nuisance algae in the tank. Coraline was growing well and so were the corals. A couple small patches of green cyano popped up and I didn't really worry too much about them. However, they've been around now for a few months and are starting to get denser and spread. I did some reading on here and it appears this is likely from low nutrients (I run an algae scrubber and over skim). So I tested nitrate and phosphate last weekend and got 0.23 and 0.04 respectively (hanna tests). Aha, I thought, just not enough nutrients! So, turned off the algae scrubber and am just letting the skimmer drain back into the sump for now. Figured that would bring nutrients up and hopefully the green cyano would subside. Tested again today and my nitrate and phosphate levels are now 0.11 and 0.00 respectively, so they've gone DOWN. The green cyano has gotten a little darker and denser, but no other algae still. What do I do at this point? Dose the tank to raise the levels, hit it with chemiclean, give it more time to see if nutrients rise and cyano goes away? Thoughts and suggestions welcome!
 

ReefGeezer

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Those readings are so low that the change you are seeing may just be testing noise. Looks like you have very low to 0 N & P though. BUT... Cyano isn't a terribly dangerous pest, just unsightly. Don't panic. Go slow. Many times, a bright green film will start to form on rocks just before Coralline starts to grow. I'd turn everything back on that was running and wait a bit. If levels don't rise, could you feed more or add fish rather than dosing?
 

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