Hello! I have purchased a 75gpd membrane to build a dual membrane/high efficiency system for my reef tank system setup. I thought I had a 75gpd somewhere already, but turns out I have a 50gpd, 24gpd, and 2 100 gpd systems. I have verified (by measuring water into the membranes and water out of the membranes) that they are both in perfect working order. (My in water is about 180ppm and the out water is 2-5ppm) If you have a verified working 75gpd membrane to trade, are interested in purchasing a 75gpd to trade me, or have some neat plant you think I would like, please send me a PM. They're really not that expensive but I figured I would check and see if anyone here was interested in it before I ended up with an extra membrane laying around.