Hi folks,just a quickie.How often should I be changing the filters on my RO unit?I've had it about 3 months and I only have enough customers to clean for a day or so a week so it's not been worked hard.The TDS reading after the RO was about 035 at the start and now it's gone up to 055.It's a 300 gallon a day one from Collins Water Products and my TDS straight from the mains is 330 or so.I'm also flushing regularly.Cheers.