Water Hardness Confusion! (long-ish)

Hi there

I have a new tank set up for Mbuna, which has been cycling nicely for
several weeks now.

Specs are :-

Juwel Rio 300 tank (300 litres, I reckon about 220 really, taking into
account displacement)
"African Cichlid Mix" gravel substrate
50 lbs of Tufa rock
Juwel "Jumbo" internal filter
Eheim Pro II Thermo 2128 external filter
2 x 38w Juwel "Multilux" lights
300w Juwel heater (plus Eheim thermo)

Ammonia 0
Nitrites 0
Nitrates 5
pH 8.2
GH 100 mg/l
KH 200 mg/l

I am currently keeping the temperature high at around 30 degrees, as I have
heard that this encourages bacterial growth.

My problem is water hardness!

The tapwater here (Central Scotland) is very soft, and I'm trying to raise
the hardness. The combination of the substrate & Tufa rock have raised it
slightly, but I don't expect miracles from it - it's primarily as a buffer
after all. I have added some Interpet Water Hardener, to very little change.

However, my problem really isn't the hardening of the water - I can simply
keep adding hardener until it's hard enough, right? But what's going to
happen to my pH level?

What really confuses me is the relationship between the pH and KH levels.
Everything I've read has indicated that a high pH level can "usually" be
associated with a high KH level. However, our tap water is very soft, but
slightly alkaline (around 7.5), and now my tank water has a pH around the
right level, but is still too soft. What can this be attributed to?

Am I worrying too much? Is my current KH/GH level sufficient for
(presumably) tank-bred fish? Should I just chill and forget about it? Should
I have listened more in Chemistry class 20 years ago?

Oh, and one last question! We're going on holiday in about 2 weeks, so
obviously this isn't the right time to start adding fish. Should I "seed"
the tank with some food whilst we're away, to keep the bacteria alive?

TIA

--
Jamesy
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