New network setup - can't see NAS on one router?

Hi there

I've recently given up on one of my reliable but super slow Apple Airport Express and replaced it with a new router (D-Link DIR-868L) - got the D-Link router at a bargain price of about £70 and I have to say I'm very impressed. Transfer speeds over my new 802.11ac network from my WD MyCloud NAS have gone from about 5MB/s to over 30MB/s at times. Great stuff.

However, I have a small problem. Previously, the Airport Express was essentially acting as an AP with an ethernet feed in. The NAS was attached to that - and was issued an IP by the DHCP server on the primary router (a slow-ish ISP router). It could then be visible across my house on both wireless networks.

The new D-Link router is, obviously, a router and acts like one as opposed to just an AP. Therefore it has its own set of IP addresses.

The primary router uses range 192.168.1.1-192.168.1.254
The secondary router (D-Link with NAS attached) uses 192.168.0.1-192.168.0.254.

The NAS can now only be seen on the second router's network - albeit with greatly increased speeds.

Ideally, I'd like it to be visible on both.

I've noticed that the secondary router can see devices on both networks - but the primary router can only see devices on its own network (it can't even see the D-Link's admin panel).

I've tried turning the DHCP server off on the D-Link router so it has to share the IP range and let the primary router assign addresses - but the D-Link router refuses to have an IP address other than 192.168.0.1 even if I tell it manually to use an address like 192.168.1.2.

I'm a bit puzzled. Maybe I'm doing something stupid but I cannot work out why the primary router can't see the 192.168.0.1 network.

Any thoughts much appreciated, thanks.