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How to lower TDS? (Mixing tap+RO?)

1052 Views 7 Replies 4 Participants Last post by  Griznatch
I'm having some initial algae issues in my newly scaped high tech. I would also like to try some crystal red shrimp in there. However I found that my tap is just outside the range for caridina shrimp. I found a zerowater faucet filter for $32. I basically creates RO water (0tds, 0kh/gh). Now I have to top off my tank (it's only 5 gallons) daily due to evaporation and because of this my TDS is around 300ppm in my tank. Out of the tap it is 192. My kh is 3-4 and gh 7-8.

If I buy the zerowater faucet filter, it claims to be good for up to 400 gal. Seeing as my tap doesn't have 500ppm of TDS, the filter should last about that long. If I use it strictly for my 5gal, that would give me enough water for almost a year with a weekly 50% water change and a gallon a week for top off.

If I buy the unit, how should I go about mixing the tap and RO to get my TDS in the desired range (120ppm)? I'm a bit confused on how this works. If I use 50/50 RO/tap, wouldn't my TDS still be 192? Or would it cut the TDS in half to 80? I understand that if I top off with strictly RO but use full tap for water changes, my TDS will just stay the same as it does out of the tap. How would using 50/50 for water changes affect my kh and gh? Would it then make me kh 1-2 and gh 3-4?

Thanks for clearing up my confusion! I'm still new to the idea of TDS as I've never really had to consider it before.

Would lower TDS have any affect on algae growth?
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TDS is typically parts per million. If you have a TDS of 100 you have 100 parts of dissolved solids for every 1 million parts of water. If you have a gallon of water with 100 TDS you can dump half of it out and the rest will still be 100 TDS.
If the filter actually clears the water to 0 TDS mixing 1/2 filtered and 1/2 tap with the tap being 192 TDS the mixture will be 96 TDS. The KH and GH will be reduced if the filter removes them. I think you better read back through the description of the faucet filter. I couldn't find where they actually stated what it removes. I think it's different than the other zero water products. They say in one place that it is not designed to remove 98.6% of TDS. Further down the page it says, " While this product can remove various contaminants the filter technology was not made to remove 100% of the total dissolved solids from your water". If you look at some of the 1 star reviews they refer people complaining back to the page with these statements and tell them they are trying to remove stuff that this is not designed for. I think you better check this product out a little better. It doesn't look like it removes much. If you could get a faucet filter for $50 that did the same thing as an RO unit for 400 gallons of water, why would anyone ever buy a small RO unit that takes up a lot more space, costs considerably more and not produce the tremendous amount of waste water that most $RO's produce. One other thing, when you add back GH and KH your increasing your TDS.
 
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