Descaling liquid choices for Gaggia Naviglio

Can I use another type of descaling liquid than Gaggia's own in my Gaggia Naviglio machine. The instructions recommend only using theirs, but it is not easy to find here in Sweden. DeLonghi and other ones are cheaper and easier to order. Are they basically the same thing and how bad are they for the environment? I read the pdfs for a few and it was difficult to see exactly what ingredients might be harmful and how.