Just done water tests and curious on pH readings

I'm curious about a variation in pH between two 50 gall tanks that I have.
Just done the tests and didn't get the result I expected so would be very
interested in your comments. Firstly I didn't expect them to be the same
necessarily but what I got was the opposite to what I was expecting.

1st Tank is a Community Tank full of plants, driftwood, fish and
unfortunately still battling with my algae. Substrate is just standard
gravel. This tank has been up and running since September. Possibly verging
on being overstocked - plans afoot to move some of the residents into other
tanks. Readings a-

Nitrates 20
Nitrite 0
Ammonia 0
pH 8

2nd Tank is a Malawi Community Tank - set up around 5 weeks ago and cycled
using existing filter medium. This has Ocean Rock and Marine Gravel plus
some crushed coral. Only four plants that are holding their own. Still
stocking with fish and it probably hasn't finished cycling yet from the
nitrite reading. Readings a-

Nitrates 5
Nitrite 0.1
Ammonia 0
pH 7.5

I use the same water on both tanks (treated tap water) and do the same water
changes on both. The pH of the tap water is 7.5.

Now, I would have expected either the pH to be the same in both tanks or
lower in the first tank because of the driftwood. Any ideas? plus might this
be indicative of a problem in one of the tanks - the first tank does appear
to fluctuate between 7.5-8.?Or is the difference down to the fact that the
second tank is still cycling?

Thanks
Gill