Aluminium in drinking water

I am in the need of some inputs about how to remove aluminium from drinking water. 

The values of aluminium shift due to the season but sometimes can reach over 300 mg/L. The idea was to test a strong cationic ion exchange resin. But the results were not quiet good enough...the performance of the filtration was below expectations...

So my question is, if the aluminium is in the complex form and not in the ionic form...since the source of the water is a lagoon and can have some amount of organic matter, even that at the moment the water treatment plant keeps all parameters fulfilling the legislation, with the exception of aluminium...Any ideas on what can I do?