Self-sustained aqua life in a 1000 Liter (250 G) tank

Hi. I am a novice in this field. I have recently built a 1,000 Liter
tank (approx-250 G, dimension 7Ft * 3Ft, 2Ft deep) in my garden
(Ahmedabad, India). It is built with bricks/mortar and covered in/out
by glaze tiles/glass mosaic. Yearly temparature varies between 5C (1
or 2 nights during winter) to 45C (1 or 2 afternoons during summer)
degree centigrades. Annual rainfall (June-Sept) 25 inches. Tank is
open to sky.

It all began 2 months ago, when I put an old bath tub in the garden
with some grass and 50 guppy fishes (1-2 inch long fish supplied by
our malaria department to prevent growth of mosquitos). After one
month I put a turtle in
it. I have NEVER fed anything to fishes or turtle. NOW, there is a lot
of algae in it.

Since past 1 week, I have (in the new tank) some water grass, some
algae, one fresh water turtle (2kg weight) and hundreds of guppy
fishes.

***I need some help***
1. I will be glad if someone could guide me to a website with "useful
advise ***AND*** Common/scientific names ***AND*** pictures of aqua
life (including plants)"

2. I would like to have aqua life in my small pond tobe SELF-sustained
with minimal intervention just in case it may have tobe left unttended
for few days whenever we are not at home.

The reason for this posting is that, most of information on net is
regarding indoor aquaria of much smaller sizes. Tips regarding
design/layout of aqua life in new tank is also welcome.

Thanking in anticipation.

- Shankar