I'll start with pH meters. Obviously, you have already worked with and have first hand experience with hobby grade pH meters. $100 meters aren't worth $100. I don't know your price range or how much emphasis you put on pH. I don't like to spend other people's money, and you will spend some $$$ on quality. Here is a link; scroll to the bottom for Thermo / Orion meters. I hope you understand that it's the guy with the PhD who chooses the equipment in the lab, not me. I will tell you this, they do not shop on price!!
http://www.coleparmer.com/catalog/product_index.asp?cls=7450
As for tweaking RO filters, that I can do. First, you need a TDS meter. I have an HM COM-100 TDS meter. Not bottom of the line, not the be-all, end-all. It's impossible to know of any improvements if you cannot measure the TDS of your water. The idea is to get the TDS as low as possible (duh) by making the RO filter work by increasing the incoming pressure. It is also important to maintain a 4:1 waste to permeate ratio in order to help the filter live a long, happy life. I use a pressure pump on my filter. My tap water pressure is about 50psi; most RO filters advertised rejection rate is based upon 70psi to the filter. With the pressure pump, I keep the incoming water at 80 psi (the pump has an adjustment on it.) In order to maintain the proper waste to permeate ratio, I put a 1/4 turn ball valve on the end of my waste water hose. Most likely, the manufacturer of your unit says to NEVER plug this line, which is true. The ball valve (never fully closed) is nothing more than a flow restriction device. As you close this valve, the pressure inside the filter goes up; as you open the valve, the pressure goes down. The goal is to obtain up to 80psi with a 4:1 waste to permeate.
I am not too familiar with the unit you purchased; I see it only has room for two pre-filters; one which should be a carbon filter and the other a sediment filter. Here is my advice: Protect your RO filter!! Chlorine will kill your RO filter in no time, so a good carbon block filter is essential. The one I use is called a "Chlorine Grabber" and is rated for 20,000 gallons and 0.5 microns. Now, you need to protect this carbon filter from sediment so it can remove chlorine. This is where a good sediment filter (or two) come in. I use a 0.2 micron filter and a 1 micron filter before that (keeps the more pricey 0.2 micron filter from being clogged sooner.) There are several good online vendors for filters. Since I use my RO filter to make drinking water, I sanitize my unit every 6 months. All filters are removed, the housings put back on, a small amount of bleach is added to each filter housing, and I turn the water on. Let if fill and sit for 10 minutes, then empty it out, run some more water through it, replace the filters, and you're done. A good ziplock back will keep the RO filter moist when you remove it from the housing.
That kind of sort of sums it up.
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