Yes you are correct. It's27  ppb on my hanna low range. On my red sea no4 pro test kit it reads .04  
Nopo-× is a form of carbon dosing. 
As to the algae not sure what kind it's thick dark green hairy patches. And o my seems to grow I  the more shaded areas. Sides of rocks fund under them. 
 
I have 6 emerald crabs 4 astro snails 1 turbo snail 1 conch snail  a stand shifting star fish with a bunch of little kinds of star fish . 
1 fox face 
1 file fish 
2 8 line fairy wrasse  
1 yellow fairy  
1 tomato clown  
1 Darf angle  
In a 80g tank 
 
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