New /Old beginnings

Pictures attached is my most recent fish keeping endeavor since 1981. Currently have a 55 gal tank stocked with 14 finny citizens consisting of 6 cory's (3 albino,3green & 3 pepper versions)
, 6 tiger barbs and 2 FM betas with 3 additional FM betas and 3 serape tetras in the quarantine tank for inclusion into the 55 family in a couple of weeks. All plants are the nasty plastic variety that are currently growing a spotted brown coating of some sort. Any insight as to what this might be and how to rid it would be appreciated, currently removing from tank and running under a hot water spray seems to do the trick.
I am a fanatic water changer and learned long ago it is one of the necessities to maintaining healthy fish. Currently change 5 gal every other day in the 55 gal tank and 2.5 gal every other day in the 10 gal quarantine tank.
The Tiger barbs delight in chasing each other and tried to do the same with the cory's but soon gave up as the spunky little cory's pushed back and the tiger barb chase ended. The FM betas are also standing their ground with the tigers pretty well.

Have monitored water parameters in the 55 and things seem to be doing well on all fronts. Local water here is pretty alkaline(7.8 to 8.0). My water PH test about the same as one of the lfs water that is processed thru a reverse osmosis filter system.
We have Petco, Pets Mart, WalM and a local chain called Pets Way here. I am particular in that I won't buy fish from any tank that has dead and/or partially decomposed fish in their display tank. Unfortunately all of these folks have that problem to some extent, WalM is probably the worst offender in that category, some difference in the 4 stores located here as to tank and fish condition. Individual on another web site made the good observation to look at fish multiple times prior to purchase at a particular supplier, this can tell you a lot plus it keeps you going into lfs frequently to see what may be offered this week.
I plan to add a total of 6 Serape, and 4 additional FM betas to complete the community. Based on various stocking calculator this will total approximately 42" of fish out of the range of calculations of 48 to 55 inches of fish for my 55 gal tank, depending on whose system you utilize. This will allow some room for growth within my tank community. Of course the are some other variables that enter in like water aeration and filtration. Currently have a UG filter system in place and a 300gph motorized filter system also.
It is quite interesting to see the minor activity change after the every other day water change, or I have a vivid imagination which is entirely possible, the population seems a little friskier, with the exception of the green cory's & the tiger barbs that are in constant motion every minute of every day.
In my holding tank with the three FM betas and 3 Serapes one of the betas has a split and partially missing chunk out of her tail fin. One of the FM betas in this group is very aggressive with the other betas and is most likely the guilty party, the tetras run and hide at the sigh of Miss Blue that chases everything in the 10 gal tank. I know from online reading that serape tetras have a reputation for fin nipping but I don't that is the case here as the FM beta is a real chaser. The 10 gal holding tank has ample plumbing fitting elbows, resin rocks and plastic plants to provide ample hiding places which beta number 3 has taken advantage of. Will be interesting when Miss Blue goes into the 55 gal tank with another dominate FM Beta that is already in residence there.

Will try to give you an update on 55 gal tank behavior with my weird mix family during the coming weeks.
Regards to all.
Fishmanbob3