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

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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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Discussion Starter · #3 ·
I suggest re-reading the description of the Zerowater faucet filter. If it's the same one I just looked up, it does not result in RO water.
I should have worded that better I apologize. It does not result in RO water, but a form of water similar in that it contains 0 TDS (as long as the filter is still good). It would be the same as the difference between RO and DI. Same result just a different method
 

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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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Discussion Starter · #5 · (Edited)
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.
Long term it's much more expensive than paying upfront for an RO system because you have to replace the filters when they exhaust. In normal intended usage of the faucet system, I'd imagine you would have to purchase their filters quite frequently considering running the tap for 1 minute wastes about 2 gallons, and the filter capacity is only up to 400 gallons and that's taking into consideration that your tap isn't super high in TDS. With high TDS I'm sure it would exhaust the filter even faster, so there's their money making gimmick. However for my purposes, I was going to hook it up to my basement utility tub and only use the filter for my 5 gal. That's only about 3-5 gallons a week. So for me, it would be decently efficient considering how small the tank is. They have to carefully word what the product does, and they can't say it removes 100% of contaminants because once the filters exhaust a bit there will be TDS present which is your indicator to change the filter. Also why they include a TDS pen. I would assume at least that's why they are using vague language in the product description. I did find a few forums where people tried the zero water for aquarium purposes and praised it, again the only drawback here is cost effectiveness versus an RO system. Eventually I'd like to convince my boyfriend to install one in the house for me, but for now to get started I think zerowater is a good solution to get my toes wet. Now let's say I do go with zerowater, how do I go about remineralizing? I want to keep caridinas, so I would need the kH to be 1 and gh 4-6. I was thinking about using salty shrimp gh/kh+ but I'm getting confused on how to use it considering UNS contrasoil also buffers pH and kH. Should I just use salty shrimp according to the directions, or do I need to dose it differently because of my aquasoil?

Alternatively do you think it would be better to use a 50/50 mix and the zerowater for top offs? If I use 50/50 and don't remineralize the zerowater, wouldn't that cut the gh and kh in half, making the tank kh 1.5-2 and gh 3-4?

Edit: I reread the description for a 5th time and saw what you were mentioning about that disclaimer. What I'm getting from this is that the pitchers are the only products of theirs that remove 99.6% of TDS, the faucet filter is slightly different in that aspect. At any rate, I should still be able to use the pitchers because of the lack of gallons I need to produce each time. I only need 2.5 for a regular water change and then just keep 1 gallon laying around during the week for top offs. Thank you for pointing that out to me otherwise I would have wasted money! Glad I posted the thread
 

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Short term, for a 5 gallon just get distilled water from Walmart. Shrimp don't typically do well with big water changes, so you'd not need much...
 

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Discussion Starter · #7 ·
Short term, for a 5 gallon just get distilled water from Walmart. Shrimp don't typically do well with big water changes, so you'd not need much...
I work a lot so having to run somewhere extra weekly or bi-weekly doesn't appeal to me. Others who have used zero water calculated the cost to be around 50 cents a gallon, so I believe it is cheaper than buying gallon jugs from the store. I've already decided I'm going to go buy a zero water pitcher tonight, that holds 2.8 gallons which is just what I need for weekly water changes. I estimated each filter will last be approximately 6 weeks and the total run cost is about $54 every 6 months so around $110 a year which isn't bad at all. Now the advice I need is to use 100% RO and remineralize gh and kh, or should I do a 50/50mix with tap and not remineralize. I'm confused on the affect my contrasoil has on pH was well, because injecting co2 with 0kh is a bad idea right? So if I use 100% RO I would have no choice but to add gh and kh to keep my pH stable correct?
 

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I don't run c02 on any of my tanks so I can't really help with that part, and all my substrate is inert. I do 50/50 with RO and tap, but I have well water and don't have to deal with city water issues, chlorine etc..
People who use straight RO usually add minerals so they can get the parameters exactly the way they want them.
I use straight RO when doing top-offs so my tds doesn't go up.
 
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