bottles, you might want to Google "how to raise KH without raising ph".
The search returns from Planted Tanks & Discus forums seem the least applicable to your situation, as they all become examinations of the OPs water for those 2 reasons, and not simply how to primarily up KH.
one thread about the subject is at:
http://www.oscarfishlover.com/forum/53-water-chemistry/130046-raising-kh?limitstart=0&start=10
Supposedly, products sold as "KH+" which
must first be mixed with water before adding to pond/tank water are best for this, as all liquid products also raise ph accordingly. Also, products are designed to accomplish this more often for Ponds than for tank use.
I'm just tossing thoughts out... do your own research- I'm somewhat of a dummy ;-)
All I did was a quick search & cursory read. You might get better info on your own, such as a product name to buy.