someone wrote:

It looks like I need to lower the PH (more acidic) around my tomato
plants. The're almost 18 inches high and are budding. The soil is
heavy clay that has had lots of compost turned in. The Ph kit says
I'm at 7.5.

You need to add more organic matter to bring the soil back to a more neutral
pH range. Organic matter produces acids when it decomposes.
So, compost is the answer.

Right - changing the pH slowly is better than taking drastic measures. A
pH of 7.5 is not ideal for tomatos, but it's also not too bad (assuming
that you're a home gardener, meaning you're not trying to squeeze the
maximum yield out of them.) They'll probably be fine - is the leaf color OK?

cheers,

Marj
--
Marj Tiefert: http://www.mindspring.com/~mtiefert/
Mediterranean Garden Advice and Shop: http://stores.tiefert.com/garden/
In Sunset zone 14-mild