So right now you are likely not having them in a cycled tank.
Ammonia tests are the most important tests for you to have, aside from nitrate, especially when cycling.
Nitrite is still important, but ammonia is much more toxic and harmful.
You are using 3 water conditioners, and they all have different compounds and all likely lie about some of the boasting benefits, such as double dosing when your fish is sick.
Adding extra
dechlorinator, whether it has aloe in it or not, will not save your fishes life.
It will not extra improve the quality of your water by dosing one condition twice and two others once.
I would stick with only one conditioner.
Choose the cheapest/your favorite, and stop using all the others.
Or, you could chose prime.
It's far more concentrated, a larger bottle, and it neutralizes ALL of those chemicals, ammonia, nitrite, and nitrate.
So it does the job of all 3 of your conditioners, but with only one bottle of treatment necessary instead of a buttload of chemicals.
I agree, it is likely ammonia poisoning.
Your 5 gallon is heavily over stocked, and it will even be considered over stocked when going to a 10 gallon.
We had a heavily planted 10 gallon, and with two adult platies and a
betta we couldn't fit much more in there withiut the bioload being really affected.
Not to mention bettas are highly aggressive towards guppies, which I assume honestly had part of the reason to do with why some of them died.
I would also like to note, taking a fish out of sick water that 6 other fish died from, doesn't necessarily mean that you got the fish out healthy before it got sick.
Humans and fish can be carriers of disease, so usually when 1 out of 7 shows no symptoms, that one could be a carrier of disease instead of just a miraculously healthy fish.
It's like having a cold but no stuffy nose, then you spend time with friends and they get a stuffy nose.
Keep the betta in the 5 gallon, and when moving up, move the platies and guppies.
The general number of fish for a 10 gallon that isn't heavily planted is anywhere from 3-6 fish depending on size.
But you don't have micro rasboras, so 6 is a terrible number.
Most people won't even put a single platy in a 5 gallon, let alone a pair of them in a 10 gallon.
I personally think 3 platies with any other fish is absolute max for a olanted 10 gallon.
And to give you an idea of sort of how planted your tank might need to be in order to keep up woth the nitrate load... Otherwise you'll have nitrates up the butt and have no way to remove them but by doing water changes multiple times a week.
My 10 gallon only had 3 fish and 2
crayfish and we still had to do weekly changes to keep nitrates below 50ish but enough so the plants could feed.
But yeah.
Do a water change now before adding your conditioner, and then figure out which brand you want to use solo, because there's not much reason to use 3-5 different chemicals on your tank every time you do maintenance, make sure you get an ammonia test, and in the future look into getting a liquid test kit.
It gives you over 800 tests for just 20 bucks, rather than 8 tests for 5 bucks! Lol
If you have nitrites you need to do a 50% water change right now.
Not doing so could have your whole tank dead in the morning.
Dont take all the nitrite out, this tank is still cycling and needs food to continue to cycle, so do a 50-60% change and then restest.
Your nitrites should be between 0 and .25, no higher than that.
I had to do 20 gallon changes on my 55 gallon when it was cycling.. Gotta protect the fish.
Let us know your testing after that.
