Choose your own adventure.

Time for some help from the community...

Problem: I have what appears to be cyano growing on my substrate and live rock. On the rock (first pic) it appears reddish with small bubbles trapped inside. On the substrate it's burnt brown extending to a slimy brown on the glass (second pic). It also appears on my koralia 1 (third pic). No matter how many water changes or toothbrush scrubs I've done over the past month, it keeps getting a little worse. I want it gone.

History: The 37gal tank is over a year old, 25 lbs of live rock, a bak pak skimmer with bio-bale (no sump), 130w of PC lighting (bulbs 6 mo old), 2 koralia 1's for flow, crushed coral as my substrate and 5 small fish. I use RO water, which I test with a TDS meter and have checked for nitrates/phosphates (both 0) - since switching to this water I've had no diatom issues (my initial bouts with diatoms looked different - more powdery, which is why I think this is cyano - unless I'm crazy ).

Temp: 78
Ammonia: 0
Nitrites: 0
Nitrates ~20ppm
Phosphates: 0
PH: 8.2

The problem started showing after I bought the second koralia two months ago and placed it on the opposite top side of the tank and pointed it towards this 'bad' side. Detritus started collecting in that spot and eventually the substrate started turning more and more brown. Since then, I've performed water changes religiously to no avail.

Yes, my nitrates are borderline high (fourth pic), which I think is the root of the problem. I attribute this to the 3 inches of crushed coral (bad decision on my part) and not shaking out the bio-bale in my bak pak skimmer for a few months (another bad decision). 20ppm does not seem that high overall, unless of course, more is being consumed by this plague and I'm getting bad readings. I also feed the fish a tiny amount every other day - not a problem.

Here are my options. Most have to do with reducing the nitrate level - the root cause *I think*.

Option a) Wait it out: Do nothing but weekly water changes and reduced light for another month. After all, tank was rock-solid stable for 10 months.
Option b) Add more flow to the bottom of the tank. Theory: Yes, flow isn't the real culprit, but keeping crap away from the crushed coral is a good idea. I'm thinking an mp10.
Option c) Ditch the bio-bale in the bak pak skimmer and add more live rock to the tank for bio filtration. Until I get more rock however, I can't get rid of this 'nitrate factory', I just need to clean it more often.
Option d) Buy a HOB refugium and stock it with macroalgae.
Option e) Last resort: Ditch the crushed coral!

What option would you choose? I'm sticking with Option (a) for right now. Slow and steady wins the race, no? Any other ideas?

 

Less food, more flow, less lights, and some macro algea

 

+1 to Newreef15

Some of that is diatoms from the addition of the new korallia, it will clear up in a week or 2.
The crushed coral is a large part of the nitrate issue - but you seem to know that already

 

+2 Adding new plastic added silicates so you got a little diatom bloom.

 

+1 to Newreef15