Looks like medium light? No macro nutriens, and no carbon source. If you can't move to a co2 set up, I would use some Flourish Excel for carbon, and you are going to have to fertilize with nitrogen(KNO3), potassium and Phospates(KH2PO4). I think you will get enough potassium from the KNO3 and KH2P04. You can look here for dry ferts if you like.
I changed my lighting to 10 hours per day with one bulb on for the full time with the other two turning on for three hours. Then I trimmed the vals that had all of the staghorn growing. Lastly I changed my dosing by adding the Excel and eliminating the Comprehensive...I'll add that back slowly. That worked really well! No more staghorn. The only algae in the tank now is just a very little green stuff on the sides...not sure why the ottos aren't getting all of that.
When I had staghorn I read that dosing iron could cause it as well as poor water flow. So, I stopped doing iron and added a powerhead. Within a week the staghorn dies and has not returned. Since you don't dose heavy, the extra iron wouldn't apply to you but make sure you have good flow in the areas that the algae is showing up. That's just my experience anyways.
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