What's the difference?

Have you tested for Po3/4? Mag, Cal have nothing to do with algae.

 

Yes, tested twice in the last 3 weeks for phosphate. But like Inwall suggested...the cyano will pull the phosphate from the water to feed on it, causing the test to read 0ppm for phos. As soon as the phos is produced, it is soaked up by the cyano.

Hey Luna, I got more tank pics (one more new leather) and a sweet vid to post later.

 

Here's the test results from a few nights ago.
KH is 10-11 (the blue turns green at 10, then yellow at 11 drops)
Mg is 1280
Ca is 360 - so I added purple up twice since then
nitrate 0
nitrite 0
ammonia 0
phosphate 0
temp 78-79
lights = dual daylight (10K, 6.7k) and dual actinic (420/460nm) 4x65 watt, less than 3 months old.

Did a 10 gal water change, siphoned the sandbed, cleaned the filter - new charcoal, new biomax, rinsed the sponges, and added 1/2 cup Seachem PhosGuard in the filter. The cyano came right back in 3-4 days! I tested the source (tap) water and very little, almost undetectable, amount of phosphate.
I've got good flow from 1 hydor koralia #3 on the left side of the tank. I took out the other #2 on the right side of the tank, bc I thought it might be interfering with the skimmer. I'm going to turn around the pump on the skimmer too, so the skimmer pump inlet isn't directly below the outlet.

 

You should becareful of Purple up, It has iodine. You should test for iodine. I dont like using all those accelerators b/c your trying to rush a natural process that takes a little time. Just my 2 cents. Luna

BTW, Purple up is not going to increase your Cal levels, I hope you know that.

 

I've also been using Kent Marine Essential Elements, which has Ca and Mg (and iodine) but how would iodine be an issue? Does iodine encourage the cyano growth?

 

iodine
Iodine is essential to many biological functions of marine creatures. It needs to be supplemented, but care must be taken not to overdose. Ask around what happens if you have too much iodine in your tank. Think about what your saying/doing. Your dosing two products that both have iodine and your not testing for it? Be very careful!!

 

what does to much iodine do luna.

 

It will crash your tank among other things.

 

I just finished cleaning the sandbed/filter/skimmer again tonight and put in 15 gallons of new water. I put new PhosGuard in the filter too. The PhosGuard balls from last week turned from white to yellow, so I'm assuming that they are doing something. I cut down on the 420/460 nm actinic lighting to see if that helps dicourage the cyano from coming back. I'm also back up to using both power heads for even more flow.

I don't think there is too much iodine. Although it's not as accurate as doing an iodine test, my cleaner shrimp hasn't molted again...

 

Phosguard has helped. 5 weeks later and absolutely no sign of cyano.