I would recommend removing the bioballs. Bioballs trap particulate matter and aren't accessible to your cleanup crew. So the trapped detritus, breaks down into ammonia. which is converted into nitrite and nitrate.
From a filtration standpoint, bioballs only provide surface area for aerobic bacteria because they float near the surface and oxygen saturated water is flowing past them. (Anaerobic bacteria require areas with no dissolved oxygen to live).
The live rock in your display has more than enough aerobic bacteria to convert toxic ammonia to (less toxic) nitrite and nitrate. Thus, bio-balls are redundant and unnecessary...and are mostly likely contributing to the bioload in your reef.
A skimmer is a good suggestion...BUT in my experience, most small skimmers don't work that well. So do a lot of research before making a purchase.
Agree with what Jim says about skimmers. I've tried 2 nano skimmers on my 26g, wasted a total of $150 Turned around and bought the BH-1000 rated for tanks up to 100g. Definitely worth the investment
I am a bit of a heretic. But, like MizTanks says - small skimmers are of dubious benefit. I run mine only after a good water change. I like to siphon up a bit of the sand bed. Not too deep, but definitely below the surface. It stirs up some gook, and the skimmer will capture that. But, most days, my bioload is not significant for the tank size. And one puffer isn't either, unless you are over-feeding it.
I don't think the puffer is the entire answer. Cut down on feeding, and definitely leave the bioballs alone. Or, like jimsflies says - remove them. And if you do - remove them quickly and completely, and don't shake their trapped water back into the tank.