I have a couple of questions:
1. By "each time I cycle my tank," did you mean each time you do a water change?
2. Do you add 1 *tablespoon* of marine salt? I would think one tablespoon per five gallons (probably more like four gallons) of water is too much of any salt. But someone please correct me if I'm wrong.
3. Did you do a fishless cycle or did you set up your aquarium on April 18 and add the fish at that time (or close). If you are cycling now, be prepared for the nitrite and amonia spikes. It sometimes take a while for it to happen.
Bioload is extremely important which is what concerns people here with the pleco and two snails in a five gallon. The amount of poo they produce requires daily water changes AND daily vaccuming of the gravel just to keep up. You might not see it, but it's there.
If you reasearch Goldfish (which I love and used to raise) you will find they do not belong in a tropical aquarium. One reason is the amount of poo but also they require cold water and are not good in a heated tropical environment. Like I said, I love them, but they are truly "dirty" fish. Also, even in a 20 gallon the Bettas will make mincemeat of their tails and Goldfish are really, really slow ... think a turtle on Valium.
If you didn't find this article in your research, you might want to check it out. http://www.tropicalfishkeeping.com/f...quarium-97842/
If you go to plecofanatics.com, you will find the general concensus is that plecos do not like/tolerate salt.
And something I discovered which really horrified me: I was occasionally feeding freeze dried tubifex worms and bloodworms. Then someone on this forum said they expanded when in the Betta's stomach so soak them in a bit of tank water first. I did...and WOW! was I shocked at how much they expanded. So, when I do feed them, I soak. Along with the above, Si and Willie eat pellets, frozen bloodworms (thawed in tank water) and freeze dried brine shrimp. They get pellets daily but the others maybe twice a week.
Hope this (or at least some of it) helps.