I forgot about the bristlenose pleco. They go well with bichirs. I kept one with a senegal bichir in a 55 gallon for years together. No problems at all.I cast a vote for flying foxes or Siamese Algae Eaters. Common plecos are not a good idea, especially considering you don't have nearly enough space for one. Common plecos get huge...like two feet long; you only have a 75-gallon tank. They also don't eat algae; they tend to eat leftover food unless they are starving.
If you want a pleco that actually eats algae, do Bristlenose plecos. They are much smaller and much more manageable (and they come with different personalization features, lol). They stay around the 5-6 inch mark, and you can have multiple, although it will be a poop fest (as with any pleco) that you will have to clean up constantly. Now that I think about it, that might be good for your plants since they need fertilizer, so the poop fest might not be that bad.