One popular way for organic farmers to reduce the pH is to mix some coffee grounds in with the soil. If you've got a cafetiere or filter machine make yourself a brew and when everything's cooled down mix a little of the grounds into the soil. Or if you're feeling really decadent just mix in some fresh (as in unused) ground coffee (not instant). But just add a little at a time and give it plenty time to break down naturally in the soil. For more info see:
http://www.homeherbgardenanswers.com/coffee-grounds-for-plants/
From everything you've said so far I think your biggest risks to a good grow at the moment are probably:
1. Shock to the plants when re-potting into larger pots
2. Shock to the plants by adding too much to control pH or nutrients
For the re-potting: Sit the big pots next to the small pots for several hours so the temperatures are the same. Ensure soil in both is moist. Try to keep as much soil as possible on the roots when transferring. Leave the big pots where they are for a while to let the plants get used to their new surrounding.
I'm not sure when the optimum transfer time would be - have you got a second set of proper leaves yet (ie third set including seed leafs)? If you move too early the root system won't be strong enough. If you go too late they will have run low on nutes and space in the small pots. You could always transfer one of the plants and wait a day or two to see how it does.
I know I've written before (above) about the dangers of messing too much trying to contorl the pH and nutes in a soil grow. Let's just say that if you added nothing the plants
would still grow, but if you add too much they
might die.
One expert says:
"
You shouldn't worry too much about your water pH and we don't recommend pH adjustment of water for soil/compost plants. Many soil growers still make the mistake of adjusting their pH when growing in soil but there really is no need - you could even be damaging your plant and its potential yield. The nutrient availability pH range is much wider in this organic environment than in hydroponics and the introduction of acidic pH adjusting liquids into these environments is neither necessary or desirable."
(see:
http://www.growell.co.uk/blog/2011/04/getting-your-hands-dirty-growing-in-soil/ )
Additives
might increase your
yield at the risk damaging the plants. But for a first time grower I would say just focus on keeping your plants alive. It's disappointing to come down in the morning and see them withering away...
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