weighting down pergola posts

[dolby123]

Hi,
I have bought a 3mx3m metal pergola and the 4 downposts are around 4" square and hollow,
rather than fixing the posts can anyone suggest what I could use as ballast to put inside the posts just to weigh them down? Sand would seem the obvious choice but wondering whether that would corode the metal, think it is aluminium but not sure, thanks

 

[Tigercubrider]

Sand might work. If it's aluminium, some reaction may take place but hard to say. Can you access the tube top?
In theory, you could bag the sand in loose bags (polythene) and drop them down. The sand would be contained by the bag. Lead shot would be heavier, but lead's expensive and poisonous.

 

[dolby123]

Yes I can access the tube top ok, putting the sand in bags seems a good idea thanks!