DIY Automated salt water mixing system

[Seth81]

Originally Posted by Zoaelite

Have you taken in account the calcium bicarbonate precipitation that will occur with highly elevated levels of both calcium and HCO3-?

I have a feeling your pump would kick out on you in the span of a day with that much abiotic precipitation.

Quoted from Randy Holmes-Farley here:

Most centrifugal pumps would not even blink if some precipitate was sucked in, however I agree that sucking in precipitate or any other non-dissolved salts should be avoided so the intake of the pump should be elevated. Alternatively I could have the pump external to the tank rather then submerged with the intake above the salt/precipitate level.


The article you cited is very interesting, I think it is relating more to how Ph effects saturation levels. I would think in my proposed setup, that once the saturated saltwater hits the RO water in the SW tank some amount of time and mixing would be required before the water should be used in the display tank. Which I have no problem with... I could program the SW tank to be filled with a mix of RO and SSW say a day or two before the scheduled water change.

I did find a yokogawa transmitter on ebay for $65 that accepts most standard probes.

[Zoaelite]

Hmmm, I was more leaning towards the point that the calcium bicarbonate would precipitate onto the impeller itself causing dysfunction.

I must be wrong if Steve had no problems with abiotic precipitation via supersaturation though.

[sphelps]

Originally Posted by Zoaelite

Hmmm, I was more leaning towards the point that the calcium bicarbonate would precipitate onto the impeller itself causing dysfunction.

I must be wrong if Steve had no problems with abiotic precipitation via supersaturation though.

I just didn't have issues with what I was doing, using different volumes or salt might change things. I know precipitation will occur eventually at some point, I just never reached that point.

[Seth81]

Originally Posted by Zoaelite

Hmmm, I was more leaning towards the point that the calcium bicarbonate would precipitate onto the impeller itself causing dysfunction.

I must be wrong if Steve had no problems with abiotic precipitation via supersaturation though.

Well I doubt it would be a problem for most pumps, but to be sure a positive displacement pump (such as a dosing pump) could be used to guarantee that precipitate wouldn't be an issue. Which would also help to ensure a good slow mixing of the solutions too. BRS sells a 50 ml/min dosing pump, based on a 7:1 ratio of RO to SSW water the dosing pump would need to be on for 3.5 hours to make up 20 gallons, which isn't too bad I think.