There are only 2 pleco that may be considered compatible with goldfish. <And that is assuming that you run your tank in the mid 70's for your fancies.>
A purist may quibble & insists on goldies be in species only tank. however, many (including me) had no problems keeping golds with Bristlenose or Rubberlip plecos. Both are dwarf varieties & won't get too big. <But you are pushing the load limit of your 180l tank if you decide to add one.> Definitely avoid common plecos (they get too big & will suck on the slime coat), and the Otos (too small, goldfish will try to eat it & the Oto's spine will cause it to be stuck in the gold's throat, killing both fish.)
If you are strictly looking at algae control, a better option may be some nerite snails (hard to find), as I find my pleco fairly ineffecient at the clean up.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.