Sphanghum Peat can be bought at a plant nursery. In my area it costs ~$4.00 a cubic ft. I put 1/2 of this in a ten gallon tank, breaking up the larger chunks 'till they're small enough to slip between my fingers, and then add water, ~6 gallons will fill the tank. I cover it and let sit. If I have time then I'll use a large utensil to "stir" it every 12 hours.

After a few days the peat becomes stratified into two layers, with a couple inches of water between the two. The first couple of weeks the lower layer will be much thinner than the upper level, perhaps even only a 1/2", but as the weeks pass more and more of the peat from the upper layer will sink to the lower layer 'till eventually more peat will be present in the lower layer.

A few days after putting the peat & water together I put a small lamp on one side of the tank. Standing/sitting on the opposite side of the tank I can see right through the tank, through the couple inches of water that separates the two layers of peat. It is the color of tea. I look around for the widest gap of water between the two layers of peat. I then insert a length of air line tubing, one about twice the diameter of the standard tubing used for air pumps/filters, down through the first layer of peat 'till I can see it protrude into the water. While doing this, I exhale slightly through the tubing so as to prevent peat from entering the tube as it is being inserted. When the tube is half way between the two layers of peat I stop, usually having to exhale a little more to clear out any small chunks of peat that may have clogged the tip of the tubing. After exhaling, these small chunks will float up back into the upper layer of peat. Then, I siphon water through a brine shrimp net into gallon containers. I usually get ~2 gallons of water out before the tube clogs up with peat. I then add two gallons of neutral water back into the tank, and repeat this process every 12-24 hrs.

It is much easier done than said. That's right, it is much easier DONE than said. In the time it took me to type this, I can siphon off 8 gallons of water at a pH value of 3.5. (I have four 10gallon tanks of peat/water, each yielding ~2 gallons of water per siphoning.)

The siphoned water has a very interesting smell. The closest description I can offer is that of Lysol, the disinfectant. Considering that this water is about the most sterile and bacteria free water there is, this smell is logical.

If you're going to do this I'd like to suggest that you lower your pH very slowly. I expect the fish will eagerly adapt to it and may even breed, but I'd not decrease it any more than .5 per day. When you do water changes, you can use the acidic water as the replacement water. Remove any carbon that might be in your filter, as well as any species of fish that require neutral or high pH water. Also, acidic water will kill plants and snails.