I dont think you have pests but there is something definitely going on. The fact that you have algea growing and becoming a problem(your words) is a redflag that maybe your Po4 and trates arent zero. The algea is consuming the additional nutrients to give false negatives on your tests. Im unfamilar with zeo dosing and how it responds to excess nutrients...maybe you should stop neo zeo for a while and see if the tank responds well. Another thought...get rid of that algea problem; Scrub off what you can, blow off what you can, get an algea blenny, add some snails, Do a lot of small waterchanges (2gallons ever 2 days), and give it time. See how your tank responds to that.