The company on ebay for the ro
units sells replacement filters for each of their units. They run from $19 up to $34 I think. A tds
meter for like $15 willt ell you when you have to replace your filters. the website says the time frame you get from each filter cartridge.
I bought this refractometer and it has proven to be very accurate and I've seen the same model on websites for $50.
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
I've bought things here and there on ebay, just be sure to use a credit card in case of a shady seller. i havent been out any money in years. depedningon what you are looking for I can probably find a online store for it so just ask. I spend hours each day browsing and researching as I have 9 tanks now.