If you use liters, figure 3.7 per gallon. I had to look it up but  
1 teaspoon = 5 ml
1 tablespoon = 15 ml
(Heck, I wasn't sure of 1 tablespoon = 3 teaspoons.)

The only time I have used baking soda (or if that isn't available, plaster of Paris) as a quick fix was when a grow out tank of young adults was getting very skittish. They can eventually "go crazy" and even kill themselves running into decorations and tank sides. That "crazy man's disease" probably better called "crazy fish disease" is sometimes a sign that the pH is either really rising (alkalosis) or dropping (acidosis). In a grow out tank of eager feeders and busy poopers, biological processes (the nitrogen cycle) will bring the pH down.

I luckily was checking the fish before running off to school. I tossed a teaspoon of plaster of Paris in that 1-gallon tank and went about my teaching duties. Much later in the day I found, to my great relief, that everyone in the tank was still doing ok. But I didn't trust that aquarium's system anymore and did a complete tear down and restart. Obviously feeding was more modest for a few days. :)

I hope that all you will have to do is add a little baking soda. adding cichlid salts may be another trick of the trade - see below.

Here is another discussion of deadly pH. I notice that PeterW jumped in on the discussion. From the San Francisco area, he has to contend with water containing very little mineral too. He was eventually raising great guppies. I'd have used his water to breed rare rainforest killies. ;)

http://www.guppylog.com/story/2005/6/8/85929/50609

Peter is one of those people who has moved very rapidly from questioner to researcher to experimenter to resource person on GL. (Of course experienced and active aquarists continue to be all four of those things.) You might Google search Guppylog for PeterW.