DI filter from LFS

[new2salt2]

ok.. i know what you are all going to say, but hear me out. *I was in the LFS and talked about a water filter for my reef tank.. they owner told me that he does not use a RO filter just a DI tap water filter. *this is the unit with a screw on filter with lids and a small spring. *he said that if i dont have a reef completely full of coral i shoudl be good using this only. *I looked and sure enough they are only using the DI filter AND HE SOLD RO too and that is why i was not suspicious with his sales pitch. *

all i have right now is a few star pollups and was wondering if you all can give me some tips. *is this a sufficiant filter for a small amount of coral? *until now i was not using anything at all.

this is a 50 gal tank with at least 60 pounds of live rock and about 10 star pollups

What was his reason he did not use RO water?
DI filters filter things out that the RO membrane can not filter and vise a versa.
Depending on your water quality will determine when you need to change the DI filter that he is suggesting. I have used these before and they are ok but they are used up very fast. I do believe they can only handle 60 gallons of water before you need to change them. At a cost of 25 bucks for one refill you will be spending more money in the long run compared to a 5 stage RO/DI system that costs around 149 which has pre filters and a RO membrane before the water even gets to the DI filter which will extend the life of the DI 4 times longer than the single DI filter you mentioned.
When you get a gallon of water from the LFS have him do a TDS meter reading to see how pure this water is.
Water coming from a RO/DI system will read 0 with a TDS.
I would think the reading on the DI when brand new would still read in the 20 ppm TDS meter test. Pure water is from 0 to 5 ppm which when combined (ro/di) is the best thing for a reef aquarium.

[new2salt2]

he said that it was not needed unless i have a bunch of coral and that he has never used one ever and has no problems with his display tank.

RO rejection rates
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I look at it this way: My corals and fish when adding the cost of these deserve the best care I can provide them. Why gamble losing any of my live stock that I have raised and cultured when I can provide a better environment for them with RO and DI water. Why take that risk?
As I said above both RO and DI together make for the perfect water solution for fish and corals.

[new2salt2]

k thanks.. BTW you got a list of what a DI only filter would remove? just to compare?

The DI cartridge contains ion exchange resins which remove the last traces of contaminants from the RO product water.
DI System provides the removal of silica, colloidal silica, phosphates, nitrates, and heavy metals.

I think it is really a big secret when coming to the % of rejection rates on the DI Because I have looked for some time now and still can't find the %'s of rejection.

I really don't think you can have a set % with the DI filters as it absorbs the impurities and depending on the water used will determine the actual rejection / absorption rate. Means the purer the water going the better the water going out. This is why it is the last filter on the RO/DI system.