Today on the BRSTV 52 FAQ, RO/DI TDS and how that can affect your filter changes.
Hi, im RT turner your host of BRSTV’s 52 FAQ where we answer all kinds of reefing questions
from our popular series 52 weeks of reefing.
This week, we are answering RM quintuple L’s question from Week 34: Reef Parameters: Our
favorite test kits explained
“What do you guys think about testing for TDS in the RO water and changing the filters
based on TDS only?.”
Quickest answer is that not all of the RO filter change intervals can be accurately
determined solely by TDS.
Filters like your sediment and carbon block pre-filters for example won't really affect
TDS, and RO membranes have such an extended lifespan that continually monitoring them
every time you make water is frankly a little overkill.
The one exception to this rule however is DeIonization resin.
Our DI resin is a mixed bed resin which means it contains cation and anion resins – each
with their own distinct charge whether it be positive or negative.
Contaminants that often show up as TDS are reduced as they bond to the surface of the
resin.
As the resin is depleted, the TDS will rise in tandem with a handy color change of the
resin alerting you that it's time to replace the media.
[split shot of resin timelapse and an elevated TDS meter?]
So if you can't use TDS to determine when a filter needs to be replaced, how do you
make that determination?
Well, it's actually pretty simple.
Sediment filters are designed to pull particulate matter out of the water, saving your more
expensive filters like your carbon blocks and membrane from getting prematurely clogged.
When this filter starts to go bad it clogs, reducing the input pressure to your membrane.
This can be monitored with a pressure gauge, like those found [X].
Once you begin to notice a drop, it's time for new sediment filters!
A few things to point out here, but sediment filters are the least expensive filter that
needs to be replaced on your system, and generally speaking the more often it is replaced the
better the lifespan of the rest of your filters will likely be.
I generally prefer the Rosave.z filters since they hold about twice as much as some other
filters before reducing system pressure.
Carbon blocks are the prefilters designed to remove chlorine, chloramine, VOCs, and
other compounds out of the water.
Monitoring them is a little more involved than the other filters, but we have yet to
find a method that offers comparable accuracy and ease.
By simply gathering some water from your systems waste, brine, or reject output, and testing
it for chlorine with a test like lamotte's chlorine test strips you can determine if
the filter is still performing properly.
If you get a reading on the chlorine test, then it likely means the carbon is exhausted
and chlorine is breaking through.
It's worth noting that if you have chloramines in your water, or would prefer an extended
lifespan on your carbon blocks, then it might be wise to switch to the Universal Carbon
block.
It is designed to remove Chloramine, and can filter up to 35,000 gallons of water for chlorine.
Lastly, your RO membrane generally will last between 2 and 5 years, but this is pretty
dependent on your water source, and how the system has been maintained.
RO membranes have a rating called a rejection rate – it is the percentage of contaminants,
in this case TDS since it is measurable, that is removed from your source water.
So a membrane with a rejection rate of 99 percent, on source water that had a TDS of
100, would most likely leave you with 1 TDS left over after it passed through the membrane.
When a membrane goes bad, that rejection rate will slip, resulting in higher TDS in your
filtered water.
That being said, this change is usually pretty gradual, so if you notice your membrane is
outputting higher TDS than it was in the past, it may be time for a new membrane.
One quick tip – a lot of folks like to use the pen style TDS meters, and while they can
work in a pinch sometimes they are too accurate for their own good.
These meters will pick up dust, hard water spots, small amount of undissolved salts,
and more from your storage container.
To prevent that, I would highly recommend installing an inline TDS meter.
These probes are mounted inside the line on your RO system and only come in contact with
the water that is being filtered, resulting in a more realistic TDS value.
Lastly, if your RO system is lacking any of these features I'd recommend checking out
our upgrade kits since they will offer the key components you need to get an accurate
pulse on most of your filters.
So simply put, not all filters' lifespans can be determined via TDS, but there are equally
simple ways to monitor those that can't
If you are interested in learning more about TDS, source water, and more do yourself a
favor and checkout Week 7: water and stuff.
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See you soon with the next 52 FAQ.