How to automatic mixing water

[wolf_bluejay]

Originally Posted by sphelps

Are you talking about building a controller for $50? I'm not sure about other controllers but to upgrade a pre-existing profilux to measure salinity you're looking at close to $400 with the sensor, the sensor alone is around $250. A two pump dosing unit to add onto a profilux is around $250 so this would be a cheaper alternative and realistically do the job just as well. I'll admit the salinity measurement is really nice to have as the options for changing and maintaining salinity are endless but I've used these units before and they require a fair bit of attention. I had to adjust the gravity offset every few weeks and often change the set points for the salt control.

If I where to go with a saturated method I would choose the salinity controller but if I was going to go through the trouble of maintaining a large amount of saltwater pre-mixed to match the tank then I would opt for the simplicity of two dosing pumps. Unless the tank was fairly large as dosing pumps would take too long to change a decent amount of water.

The cost I was referring to was to build a simple controller for the salinity only -- not a whole controller -- and the $50 for the parts was an over-estimation. As for the cost of the salinity probe, the hardware is really only worth about $50-$100 for the probe. It would be even cheaper if you didn't bother with the "automatic temperature compensation" and assumed that your tank would not vary from 0-100 degrees.

Most of the profilux and other controllers are really, really pricey for what the hardware inside costs. Similar boards that support sensors, probes, relay outputs, and all the fun stuff are usually under $200 for the whole works. The extra cost is for making it pretty, including programming software, and customer support.

As for the peristaltic pump -- I just don't think they are quite up to the task of moving 50 gal a week of water. These pump are built to part time, and moving small amounts of water accurately. replacing a $250 pump about once a year adds up quickly.


I think that most of this was relating to the larger tanks, and larger equipment rooms/areas as I don't think I would go through the hassle of auto water changes on a 30 gal tank. I assumed that most people looking at this were in the same boat as me -- where doing 20-30 gal water changes a week just doesn't work with a bucket. If I could do my whole water change using 2 old salt buckets, I would go that way. But when you need 30-40 gal tubs just to mix the water -- 200 gal of water storage isn't too crazy when you have a 200+ gal tank and all the other gear that goes with it.

[golf nut]

I'm getting intrigued.

If I poured a gallon of ro/di water into a bucket containing 4 gallons of salt crystals then I anticipate that the solution would saturate then become stable, if I removed a known amount of that solution with a double acting cylinder and mixed it with ro/di in the correct proportions I should have a proper mix to be able to inject into the aquarium, if I then replace the saturated solution that I removed with more ro/di and at the same time remove the total mixed solution from the display tank and then repeated the process I should have a fairly accurate way of doing a water change , correct?

[sphelps]

Correct, so when will the prototype be ready?

[golf nut]

Originally Posted by sphelps

Correct, so when will the prototype be ready?

I am installing a swamp sump, hopefully soon.

When you mixed a saturated solution with excess salt always visible was the SG very constant? roughly what percentage of RO/DI did you add to get you to required levels?

[sphelps]

Originally Posted by golf nut

I am installing a swamp sump, hopefully soon.

When you mixed a saturated solution with excess salt always visible was the SG very constant? roughly what percentage of RO/DI did you add to get you to required levels?

If temperature remains the same then the saturation level remains constant meaning a constant SG as well, should be about 1.200 at room temp.

Saturated saltwater has a density of approximately 1.2g/ml at 21 degrees which is around 265ppt. Lets say you have 1L of saturated solution and your target is 35ppt. This means you'll need about 6.5L of fresh water to be added. So for every 1L of saturated salt, add 6.5L of fresh water.

[golf nut]

I think its time to do some testing with a 4 head peristaltic pump.