A few question around my fishtank?

I have a 10 gallon tank with a dieing plant, 1 mini crab, 1 mannish beta, 3 sunset platies, 2 cory fish, 2 silvertip guppies.

Is there anything wrong with this combination of fish?
What temperature should the hose down be?
How often do I have to change the marine and how much water should I change?
Can I add anymore fish?

Bettas usually shouldnt be with guppies or platies. They should nip at them relatively a bit.

You didnt mention if you had a filter or not... But you do. And all of your fish are also tropical, so you stipulation a heater. As with all tank, you should change a portion of the water weekly. With a 10 gallon, you might just want to switch like 10-15% of it.

No. No more fish.
The male beta can be aggressive towards other fish and can nip their fin. Most people hold on to in a little 1 gallon tank which is pretty well-mannered. The Temperature should be around 70degrees faireinheit( srry about my spelling). You should do a 25% water change almost every 2 weeks or so. So change about 3 gallons or so. If you want to add anymore fish trademark sure you dont have over 10 inches of fish in in attendance.
Hope it helps
Answers:    The plant is any lack of UV light or the Platies are eating it. 3 is the recommended minimum number for Cory and they don't really walk with a crab due to a conflict at feeding time. Platy could fin nip the Betta and the Betta could fin nip the Guppies. You will obligation to keep an eye on things.

Temperature should be 26C because you have a Betta in the container.

20-25% water change once weekly.

No more fish the Platy will no doubt breed as possibly the Guppy and you are around at max anyway,
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