The problem may be a misunderstanding of a regular 20 gal compared to a 20 gal high. The surface area of a 20 gal high is less, which equates to less are for oxygen exchange.
I ran some quick numbers on AqAdvisor for you. Of course, this is recommended and we would need to know your filtration equipment and etc to get a better feel, but I find AqAdvisor a decently fair calculator.
Current Stocking Level:
Suggestion: If you want to keep more than 1
Molly, minimum recommend male to female ratio is
1:2 (M:F). You will be less likely to experience problem if you get even more females.
Recommended temperature range: 77 - 77 F.
Recommended pH range: 7 - 7.8.
Recommended hardness range: 11 - 15 dH.
Recommended water change schedule:
30% per week.
Projected Stocking Level:
Suggestion: If you want to keep more than 1
Molly, minimum recommend male to female ratio is
1:2 (M:F). You will be less likely to experience problem if you get even more females.
Warning: Water temperature requirements are not fully compatible between all selected species.
[SIZE=-1]=> 64.4 - 82.4F: Molly[/SIZE]
[SIZE=-1]=> 71.6 - 77F: Harlequin Rasbora[/SIZE]
[SIZE=-1]=> 77 - 82.4F: Julii Cory[/SIZE]
[SIZE=-1]=> 78.8 - 86F: German Blue Ram[/SIZE]
Recommended pH range: 7 - 7.
Recommended hardness range: 11 - 12 dH.
Recommended water change schedule:
33% per week.
All Molly quantity:
Suggestion: If you want to keep more than 1
Molly, minimum recommend male to female ratio is
1:2 (M:F). You will be less likely to experience problem if you get even more females.
Recommended temperature range: 64.4 - 82.4 F.
Recommended pH range: 7 - 8.2.
Recommended hardness range: 11 - 30 dH.
Recommended water change schedule:
49% per week. (You might want to split this water change schedule to two separate 28% per week)
Your aquarium stocking level is 141%.
Your tank is overstocked. Unless you are an experienced aquarist who can meet the maintenance/biological needs of this aquarium, lower stocking levels are recommended.
