I tried a Betta once in my 33g together with 20 cardinal tetra. Went fine for a couple of weeks...
After that almost all my cardinal died within a week (missing body pieces so not due to illness).
Never saw my Betta being aggressive to them...but am sure it was him.
Corries do not attack tetra...
Usually I know already what I want and how it looks like. In most cases even will look up how to tell the difference between male and female.
But this time it was a spurr of the moment thing since it was the first time in I saw them there...
I sometimes look into the vile when putting it on top of the test paper...
shifting it over the colours and looking for where the difference is the least.
Always use daylight though...artificial light makes it more difficult to compare.
Too hard to tell from those pictures for me.
Female, once old enough, would show a pinkish belly and I do not see that in any of your pics.
Added two pics of a male and a female.
Male is swimming to the left
Typical ways to spot the difference is the tip of the dorcal fin that is much longer...
Hope you have a spare one. I kept the original heater that came with my tank as a back-up.
From time to time I still use it when I need to setup a quarantine tank (so know it still works).
Also came in handy when we moved a few months ago.
Could setup a temporary tank in my old place...
Fluval E series here. 3 years with no issues at all. Has digital display that tells the temp. and also changes colour when it is below or above the set temperature (red- green - blue). Also informs you when the water flow is not sufficient (near it).
Here are pictures of a male and a female.
Female has pink belly, fluorescent dots in that black spot on their side (under their dorsal fin), and the front of their dorsal fin (black part) is less long compared to males (with males they stick out like a lot more)
Last one is not really visible...
It IS overstocked!
For sure a pair of Angels need a lot more room in a month or two.
Also...having the Betta and all others (except for maybe the corys) is not a good idea. They will fight to one dies sooner or later
Only a few succeed in having a betta in a community tank.
oooh....sorry to hear that.
If I give my fish frozen food I put the cube in water test tube first (that contains tank water) and put it on my hood for a while (so the lamps help to defrost it).
But I also had deaths in my tank for no apparent reason.
Just keep a close eye on all others...