Well for the return on the tank I purchased a 3/4" to 1" male adapter and I unscrewed the barb fitting on the Red Sea return fitting. I then wrapped the threads on the male adapter with teflon tape (10 turns, yes its a lot). The Teflon helps seal the threads as they are not the same. So the male adapter gets screwed where the barb fitting was.
As for the reactor, you will also need male adapters. I believe they were 1/2" plus a set of o-rings.
@Broadfield has this step very detailed and honestly I don't remember the exact size of the o-rings. However if you search his thread its all on there.
This tank was taken down in the 2017 after Irma hit FL so I cannot get you any pictures.
I do however have a new tank I just set up and I went a different route with converting the metric piping to standard pvc. I used a metric to standard union from Coralvue to make the conversion. Much solid and I think easier. Here is a picture. The barb fitting also needs to come off but this time you cement the union to the Red Sea fitting with abs to pvc cement.