hi i bought this system last summer, when i had this system it filled 1000 ltr in about 5 or 6 hours after couple of months slowed right up i back wash every time i use it im on my second ro membrain . why is this so slow water presure ok i know its cold so will slow up. pre filters new . iv got mates who have the same system and theres are working 3 years on still fast are they cheap ro/s now? any info guys im lost