Martin,
Per your request, my comment..
If I understand correctly, you have an algae bloom at 33 feet. If that is correct, to me that means sunlight is reaching to the bottom. IMO one option for you might be to plant a short vegetation species that is endemic to your area. That will help use nutrients and reduce the food available for the algae. That should improve clarity in the long term IMO. The vegetation will also provide oxygen during the day and provide habitat should you ever want to enhance your diving experience with a fish population to observe.
Good luck and please post some pictures/videos if you get the chance.
Bill D.
Last edited by Bill D.; 08/21/16 09:13 PM. Reason: Clarification