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Old 08-23-2011, 01:18 PM   #1
BucketsII
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DI Filter and effects on Ph


I was tired of buying 1-2 gallons a day of distilled water to top of my sump so I visited my LFS and he talked me into a DI filter (no RO) LFS said that the RO would waste 3 gallons for every 1 filtered and since water is very expensive here I went for the DI.
After a couple of weeks using it I find that it lowers my PH and I have to add buffer every couple of days. Don't remember the brand but it is a part a and b product.
Is this normal? Am I doomed to adding ph buffer forever?
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Old 08-23-2011, 01:34 PM   #2
AZDesertRat
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I can't believe they sold you a DI only system. Most of the wate rI am aware of in Florida is pretty high TDS so DI will not last long and get very expensive to replace.
When you calculate it out, I'll bet you a buck the cost of producing RO/DI water is still less than a nickel a gallon including the water and sewer rates and replacement filters, its not as expensive as some make you believe.

Some DI resins will have an effect on pH depending on the cation/anion blend but its no big deal. The DI water takes on the pH of whatever you add it to and a couple gallons in a larger system should not have any permanent effect of pH.
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Old 08-23-2011, 02:40 PM   #3
BucketsII
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Than something else is causing the PH drop. Can it be I have no fish in the tank? Waiting for ich cycle to finish.
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Old 08-23-2011, 02:45 PM   #4
BucketsII
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Figured out from my water bill that I am paying 2.5 cents per gallon for water and sewer. LFS told me $20 for resin on DI cartridge and that it would last me 3 months so that would be 5.2 cents a gallon. That is acceptable for me at this point. If I add the RO unit it will cost me another $130 and that goes a long way in DI filters.
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Old 08-23-2011, 02:50 PM   #5
raskal311
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If I recall correctly RO/DI water is 7.0-7.2PH.
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Old 08-23-2011, 03:14 PM   #6
AZDesertRat
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You really cannot accurately test the pH of RO/DI water, there are too few ions to measure and it is volatile at that point. CO2 in the room or air will show up and have an effect on your tests.

Do you know the TDS of your tap water and if it contains any dissolved CO2? I seriously think your LFS is mistaken on his resin estimate. Watch it carefully with your TDS meter to see ehat you actually get, I'm 100% convinced it will be much less than his guess. More money for him I suppose.....

I'm not trying to be negative but I see this all the time and it usually results in a disillusioned hobbyist who soon gets out of the hobby feeling he was betrayed or lied to. You can just about figure one pound or 16 oz of nuclear or semiconductor grade mixed bed resin will last right at 3000-6000 total TDS in the real world and its usually on the lower end.
Say your TDS is only 100 out of the tap which is much less than the national average TDS of 250, 3000/100=30 gallons of 0 TDS water before the resin is exhausted. Even figuring the high end of 6000, 6000/100=only 60 gallons of treated water. $20 for replacement resin / 60 gallons = 33 cents a gallon.

In reality it will last about 25% longer than that because a properly packed 10" vertical DI canister and refillable cartridge hold 20 oz not 16 oz but the pound is easy to work with.

I hope I'm wrong in this case but I've been doing this a long long time and doubt if I am far off. A handheld TDS meter will tell the tale.
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Old 08-23-2011, 03:36 PM   #7
BucketsII
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so I need to get a RO and add it to the DI so the resin can last longer?
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Old 08-24-2011, 02:09 PM   #8
AZDesertRat
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Reverse Osmosis does 90 to 98% of the treatment, the DI should only act as a final polishing filter to get what RO misses. Without RO, DI resin does not last long at all. As an example, even with an RO in front, if the RO membrane is only operating at 96% rejection rate or removal efficiency versus 98% efficiency you cut the life of the DI resin in half. Just 2% makes that much difference so imagine your DI life with no RO treatment.
If you can only afford one or the other, RO is the much better choice since it is the workhorse.
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Old 08-24-2011, 02:19 PM   #9
FutureDoc
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Yes. AZ knows his water.

You will likely not see as big of a jump in your water bill as you might think. Fla water really needs a good RO/DI system.

When I lived in upstate SC, we had TDS of about 40-60 straight out of the tap. This was very good water quality for tanks but even with a DI alone, it would last for 35 gallons at most for 0 TDS produced water (did it for setting up a tank at my office). It would quickly rise after that.

Definitely go with a RO unit, it will be much better that you might think
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Old 08-24-2011, 02:38 PM   #10
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I'm not sure if this is your water provider or not:
http://www.pinellascounty.org/utilit...s/CCR_2010.pdf

Look closely at the report though and you see things like the water is a blend of wells, surface water and desalinated sea water so the quality can change without notice depending on the demands and the blends. More noteworthy is the fact they add phosphates to the water to control corrosion in the distribution system piping. This is of special concern since we do not want phosphates in a reef system. RO or DI alone will not remove phosphates, it takes the combination of both and the DI resin must be very high quality and have good contact time. Running tap water through the resin will not remove it since it must be very slow, a trickle really, for good contact time and without the RO to remove much of it DI won't stand a chance.
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