Alright i have like 15 minutes so here i go,
You need plants and more plants,
Seeing as you live in brazil i would say the climate will support a Banana Tree,
Here is a link were you can see one growing in a pond here in the US,
http://www.bonniesplants.com/banana.htm
Also The climate will support some Egyptian papyrus,
This will get huge placing a large amount of shade on your pond Lowering the algea hopefully,It will gorw to about 8 Feet Tall DO NOT GET THE DWARF VARIETY IT WILL DO YOU NO GOOD!!!!
http://www.bonniesplants.com/PondPlants.html
If your a Good botanist you could try to cultivate some Amazonica Victoria They get huge there the GIANT waterlily,
http://www.victoria-adventure.org/
And as for the Ph banana trees Thrive in High ph and will eventually absorb alot of the High Ph but thats only if you can stop the Leak of ph into your pond,This could be from Relativly new concrete sealent or such or alot of rain,
Nitrogen will be resolved by the plants or you can go and buy whats called a Degassing Column Which will Help lower the nitrogen,And other bad gasses,
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/7855/cid/2005
AS for the lack of filtration i would reccomend Plants plants and more plants,
But if this is not possible i would reccomend a Large Bioreactor By clearwater for a pond that size,
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/7831/cid/2002
If this is not possible there is something called a Niagra Tower By clearwater,
This will help also,
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/12713
But also you can get a RBC (rotating biological contactors)
This would work for you i believe,
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/4892/cid/1379
And Get some water movement going it looks "still"
Well i gtg,
Andy