Using anion resin only

[richard203]

Hi my tap water have high nitrate and I'm just using anion resin only and chlorine filter to filter the water. Now my water is 0 nitrate. My question is after using this method my fish started dying. Im ordering a high ph test kit to test the water to see if that is killing my fish.

 

[Randy Holmes-Farley Verified Community Expert]

Unfortunately, that result is what I would expect. You should never use just one type of resin.

You have to understand how a DI filter works.

The anion part of a di swaps out all negatively charged ions and replaces then with hydroxide (OH-). That effluent has super high pH.

The cation part of a DI swaps out all positively charged ions and replaces them with H+. That effluent has super low pH.

When those two solutions combine, the H+ combines with the OH- producing H2O

h+ + OH- --> H2O (water)

leaving the final effluent without any ions and at mostly neutral pH.

You tank is likely very high in pH and alkalinity right now. Precipitation of calcium carbonate is bringing the pH and alk down now.

I think a big water change is in order.

 

[richard203]

Unfortunately, that result is what I would expect. You should never use just one type of resin.

You have to understand how a DI filter works.

The anion part of a di swaps out all negatively charged ions and replaces then with hydroxide (OH-). That effluent has super high pH.

The cation part of a DI swaps out all positively charged ions and replaces them with H+. That effluent has super low pH.

When those two solutions combine, the H+ combines with the OH- producing H2O

h+ + OH- --> H2O (water)

leaving the final effluent without any ions and at mostly neutral pH.

You tank is likely very high in pH and alkalinity right now. Precipitation of calcium carbonate is bringing the pH and alk down now.

I think a big water change is in order.

so should I do cation -> anion or anion -> mix?

 

[Randy Holmes-Farley Verified Community Expert]

so should I do cation -> anion or anion -> mix?

Both work. The latter may be good for well water with elevated CO2. I have only ever used mixed beds since my water does not have excess CO2.

 

[mcarroll]

Someone screwed up our RODI with a lone cat or ani DI filter and I could never keep corals happy. Strangely it didn't show up on pH tests or anything else we tested. It got figured out when the media on the filter was changed the next time and we could see what filter cart was in there.