Welcome to the forum! Unforunately, there are some issues (obviously), but luckily they are easy to solve.
Do not use any meds. Firstly, do a large water change. Make sure you put the conditioner in the water before adding it. Ammonia builds up in those tanks, and in an uncycled tank that is stocked like that , you should be doing 50% a week and a 100% once a month.
Secondly, freezedried foods are not that great, and you should be feeding 2-3 pellets (pre soak them all the way before feeding) twice a day. Since you also have to feed your cories, you'll probably have some ammount of excess food which should be removed after the proper ammount of time. Food that is left is will rot and produce ammonia.
Thirdly, corys need to be in groups of 4. Because of this, you want to cycle your tank, because 5 fish in an uncycled 10 gallon would be a lot of water changes. After you cycle your tank, you'll want to get two more cories. Since you already have fish, you should do a fish in cycle. Here is how: Leave your filter running all day every day. If you are using carbon filters, that's okay, just leave the filter media in there and do not remove it. Stuff your filter full of sponge filter media, which you can buy for like 2 dollars at any petstore. Once again, do not toss it. Once a week you'll want to do a 50% water change. Stir up the gravel or use a gravel vaccuum to get the gunk out of the gravel. If you notice your fish acting funny, do a 50% water change ASAP. Once a month, during one of your water changes, take your filter media out and swish it through the old tank water to remove some of the gunk that builds up.
In a cycle
, benificial bacteria grows in your filter media and on your tank surfaces and they convert your ammonia to nitrites and then to nitrates. Of the three, nitrates are the least lethal and build up the slowest, so once you have your water cycled, you only have to do a 50% water change once a week. You'll probably want an API Master Test Kit
to monitor your water quality. There should be less than .25 ppms of ammonia or nitrites throughout the cycle, and once you are complete, you will have 0 ammonia, 0 nitrites, and visible nitrates.
As for your cories, you will want more cover for them. Bettas are like school bullies... they either ignore the fish or attack. Sometimes they will ignore for the longest time then decide they no longer want tank mates. As such, you need to be prepared for this and have enough hides for your cories should they need it. I suggest silk plants for cover as well as possibly a few easy live ones
Wow, I'm sorry for the super long type and a super long read... and it seems like Vaygirl got here first, but I hope it helps!