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How to prep RO/DI water for plecos?

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Post Wed May 14, 2014 7:16 pm
Guysmiley User avatar
Level 3 Member
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Posts: 87
Location: St. Paul, MN- Grand n Dale
Until now, I have been using a R/O filter given to me by a friend for my L046 zebra tank water. I would add Replenish, by SeaChem, to replace the minerals removed by the RO filter. I've bought a RO/DI filter and was wondering if Replenish is good enough for the addition of a DI filter? I've never dealt with DI water and wanted to make sure it is safe for fresh water fish with just the addition of Replenish.

Also, is there a more economical mineral additive out there? Thanks for your suggestions.

Post Wed May 14, 2014 7:41 pm
Passionfish Level 20 Member
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Posts: 12021
Location: apple valley, mn
This question is quite complex and requires a through understanding of water chemistry as to why the following values are important. Some keepers can cookbook it with out understanding basics. For now, here is the cookbook approach.

What is needed to determine if water is right is:
TDS /conductivity meter. Tests for divalent ions (general hardness) and alkalinity (KH or carbonate hardness).
May or may not need DI filter post RO membrane. Excellent RO/DI systems will produce water at zero to 2 ppm TDS. As already pointed out, this water is not correct for breeding plecos and needs to be rebuilt. If RO membrane removes all divalent cations, then adding DI unit is not needed and should only be used if total TDS is greater than 50 ppm.

Desired water needs to have pH between 6 and 7.5
TDS needs to be 50 ppm or less.
GH is best if zero. If RO membrane is insufficent to remove all divalent ions, either replace it, add DI unit or try filtering RO water through peat.
Carbonate is necessary to buffer water and avoid pH swings. Test for carbonate be sure there is carbonate present. If no carbonate is present, do not all salts that contain calcium carbonate. Use sodium bicarbonate. Total TDS needs to be 50 ppm or less.

Unfortunately, there is pleco salt mix to add to pure water.
Like a complete unknown

Post Wed May 14, 2014 7:56 pm
Guysmiley User avatar
Level 3 Member
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Posts: 87
Location: St. Paul, MN- Grand n Dale
Thanks for the info Passionfish. It sounds more complicated than I thought. I just bought my first tds meter the other day and it arrived in the mail today. I still haven't opened it. Sounds like I have some studying to do.

Post Thu May 15, 2014 3:48 am
Passionfish Level 20 Member
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Posts: 12021
Location: apple valley, mn
It is probably easier than what I wrote.

1. Get divalent ions out. Calcium and Magnesium Accomplish with RO alone or RO with DI and/or adding peat to water in storage.
2. Get TDS down to 50 ppm Accomplish with RO unit, may need to add DI unit.
3. Have some carbonate in water to buffer pH. If water does not test for some carbonate, add very small amount of baking soda. Retest water after adding baking soda for TDS and alkalinity.
Like a complete unknown

Post Thu May 15, 2014 10:05 am
mke User avatar
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Posts: 435
Location: Saint Paul
This question is quite complex and requires a through understanding of water chemistry...


Okay, I'm leaving now. Let me know when there's some pretty pictures to look at. THOSE I understand.
"He who has a why to live can bear almost any how." Netzsche
"Old aquariests never die. They just begin to stink." mk
"So many fish; not enough outlets." mk


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