How does that have to do with anything? Well yes S. american cichlids have no argument with bichirs as long as they stay in a reasnoble size tank and the fish does not get too big....However,Cichlids can be very agressive and with the passiveness of most diurnal bichirs they may be bullied fairly often....I as always would give you the too small rant....As I can imagine this is your 30gal which is to skinny to house a bichir IMO/IME long-term unless it does not exceed the length of 6".....
Salvinis can be really aggressive, among the smaller cichlids I'd put them right there with convicts in terms of aggression. You might be OK...lots of cichlids, even aggressive ones, will ignore things like bichirs, plecos, things that don't look anything like another cichlid. But it's iffy...I probably wouldn't try it unless I had a backup plan, ie another tank where I could move the sal or poly if there's problems.
IME larger bichirs, those 8+" are fine with ll but the most aggressive cichlids. Even with the typically aggressive cichlids bichirs, like most bottom dwelling fish, are ignored.
In a large enough tank there will be no issues. Ideally the smaller upper jaw species should be kept in 75 gallon tanks or larger as adults. The footprint on a standard 75 gallon tank works out very well with the smaller species of bichir.