While suitable for most purposes, the vast majority of tap water simply isn’t suitable for keeping delicate marine organisms due to organic and chemical pollutants. Using an RO (Reverse-Osmosis) Unit is a simple way around this and these days units are obtainable at a very reasonable price.
However, an RO Unit does require some maintenance to work well over the long term. As membranes clog and DI resin becomes exhausted, traces of undesirable substances can creep into your supply and even result in undesirable effects in your reef. This is where a TDS meter can be really handy! Coming in most cases as either handheld units, or inline devices, TDS meters measure the total dissolved solids present in a water source. With RO Units stripping water of such substances, they are ideal for determining if the unit is performing well.
The DM-1 from RO Man is an inline unit costing only slightly more than many handheld units. Unlike handheld units, you won’t have to root around to find this device as it is integrated into your RO unit. Basically you can just insall it and then forget about it until it comes time to check your levels. Simple instructions show exactly how to fit it which is really simple even with an RO unit that is already set-up. Although we found we had to be quite careful where we placed the unit due to the length of the wires running from the probes to the display, the unit did prove to be extremely versatile and we could even use it effectively on our system which has been ‘teed-off’ between the membrane and the DI cartridge (when using an RO unit intermittently this can help to prolong the life of the DI resin). Our unit showed us that our feed water had a TDS of 285ppt, and our product (after the membrane) fell from 093 to 006 after around 5 minutes (we run the unit intermittently, plugging the tubes when it is not in use). After the DI stage the TDS reading dropped to zero. These readings very closely matched those attained with a handheld meter.
Once in place, this unit features an automatic cutoff so the battery should last for a long time. We think a back-lit display would have been nice but it’s not a major problem as we keep a small torch near our unit for inspection purposes anyway (again, consider where you locate the unit though).
Overall we really like it… simple to install, excellent price and accurate readings straight out of the box.