Does ROD water cause Precipitation?

[Nikolai_VN]

Hi fellow reefers.
I’ve been struggling with precipitation for years and didn’t know why, it happen from time to time and cause my Alk and Cal to depleted, both happen with Dosing or Calcium reactor.
After 3 months of fighting, water change, my tanks is completely crash due to my stability is out of wack, i cant control Alk and Cal anymore because the more i dose or tune the Cal Reactor, the faster it depleted, and precipitation show in everywhere in the sump, and the glass, even the sand bed become a rock bed because of precipitation, pump and powerhead stuck and broken. How frustrating huh .
After changing every method i know to prevent it, i’ve failed, and in final act, i shut down the Rodi top off.
After a week cleaning and crashing the tank, it stop. I watch it for a month and it completely stop.
Now i have to mixed saltwater to top off my tank, and it fine around 1025-1027, depend how much or less salt i mix.
So if Randy can explain it, i’ll glad to learn more.
If you guys are having the same issue, i’ll be glad to help.
Thank guys for reading this, and sorry for my broken English.

 

[Randy Holmes-Farley]

The addition of pure fresh water to replace evaporation in a reef tank is not going to drive a precipitation event.

What do you think the alk and pH are, and how are you measuring them? High alk and pH are the usual drivers, as is low magnesium, low phosphate, low organics, and very high calcium.

 

[Nikolai_VN]

The addition of pure fresh water to replace evaporation in a reef tank is not going to drive a precipitation event.

What do you think the alk and pH are, and how are you measuring them? High alk and pH are the usual drivers, as is low magnesium, low phosphate, low organics, and very high calcium.

Hi Randy, thank for replying.
I use Apex so i can watch PH swing in daily basis. When the precipitation occurs, Ph is around 7.9-8.0.
I test my parameters by:
Cal and Mg: Salifert
KH and Po4: Hanna.
No3: Nyos
I use Fauna Marin App to calculate my dosing schedule.
My start point is:
Cal: 360
Mg: 1028
Kh: 6.9
No3: 0 - 5
Po4: 0.01- 0.03
I’ve raised them up to:
Cal: 440
Mg: 1380
Kh: 8.5
Then the precipitation happens and it requires more and more dosing fluids and it out of control when Alk and Cal began to drop although i dosed more than 200ml a day for 500L tank.
Please notices that after i turn off the Rodi ATO, it stop the precipitation and my tank is running normally til now (a year)
Now i can dose or tune my Calreact to almost over dose but it slightly precipitation occurs, however I doubt that if i keep top off by Rodi.

 

[Randy Holmes-Farley]

My suggestion is to measure alk and pH some other way to double check those values.
But in general, this is my advice to stop the cycle of precipitation, which for you includes stopping the reactor for a while.


1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline to 7 dKH.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.