Third fish for 20 Long damselfish dungeon

[PocketClam]

I currently have a spingers' damselfish and an occy in my 20L but am considering adding another fish to the display (I have allot of live rock and a fair few large cave-structures), I'd really like something which might occupy the open-water or the top of the column but I'm not really sure what to go with.

I know Chromis *can* work out okay in the long-run with damselfish and that springers' are some of the least-aggressive damsels out there, I was also considering the possibility of trying to add a royal gramma or a chalk-basslet (since they should be able to hold their own ) but they're both semi-cave dwellers and not as active as something along-the-lines of a lemon-chromis. A possum or pink-streaked wrassse isn't totally off-the-table either, as I have an acrylic-lid, but I'm not totally-sure whether they* would become problem-fish down-the-line because of their aggressive-tendencies as adults, they also don't really occupy the area of the tank I'm trying to fill.

Another consideration was just to go with an additional less-aggressive damselfish like a neon, talbot's, or randall's, but I've heard Talbots, while peaceful with other fish, can actually be aggressive towards other damselfish species and randalls are pretty difficult to come-bye.

Was hoping to get some insight and advice, I'd really like to increase my bioload so I can stop dosing nitrate and phosphate just to stay above-0.

 

[Peach02]

if your looking for something to occupy the open water in a 20 long id recommend a pair of clownfish or a wrasse of some kind. the clowns will occupy a corner often if they don't host something and a wrasse will be all over the tank throughout the day.

 

[Tamberav]

Pink or possom are generally shy and cryptic. Not aggressive like a sixline. They hug the rocks.

My Gramma is out all day....he just hangs out on his side of the tank but totally visible in the open.

When I had a Talbot and spinger together they constantly bickered.

 

[PocketClam]

Sounds like a wrasse or a Basslet are the best options, I'd read that Talbot's (while peaceful) didn't care for other damselfish, good to know that's probably the case.

Any thoughts on the chromis idea? Too big or potentially-aggressive later on in life or would likely end up the victims as big targets and potential-pushovers?