Welcome!
I would strongly recommend making your own water as it put you in control and is cheaper in the long run.
You don't just need to fill the tank once, but also have a supply for water changes.
DI is an ion exchange resin pod that fits after the RO system. Many suppliers will sell both together but you can get them separately.
Personally I have very soft tapwater so I don't use RO and just have a big DI vessel.
Hope that helps a bit?
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