I tried 2 with mine, the rays ate them at about 4 inches long. The bristlenoses tried to keep out of the way and did not bother the rays. I was worried about them getting stuck in the rays throats as bristlenoses lock out their pectoral fins when under attack and stay that way even after they die.
I would not worry about added bio load, bristle noses even when full grown are small (under 12 inches often under 6) and the bio load they put out would be a sneeze to a ray. I am not risking any more with mine though.
Have you tried decreasing the nitrate to under 30ppm, reducing the light hours and maybe add some pothos plants to out compete the alage. I only need a quick few seconds with an algae magnet (get one that floats) and that is it once per week.