How to automatic mixing water

[abcha0s]

I'm going with the ~200 gallon storage container. I'm looking at the LiterMeter III peristaltic dosing pumps for the Continuous Water Change. The pumps are calibrated by volume, rather than time so minor differences in pressure can be accomodated. The ATO runs independantly and has nothing to do with the water change system. It's an incredibly simple system.

However, the purpose of my post was to share my experience with salinity probes. They are increadibly sensative to stray voltages and tend to wander all over the place. Curt at Apex recommends that the salinity probe be placed in a drip cup to completely issolate it from the sytem. I was never able to get a consistant reading from my probe and basically threw it out.

Another concern is the mixing rate of new saltwater coming in with tank water. I use this concept to monitor the pH of my system when topping up with Kalk saturated water. I have the controller set to shutoff the Kalk ATO when the pH hits 8.4 - However, by the time the pH sensor reads 8.4 the pH in my tank is past 8.5 - There is a delay in the reading but it's also partly how the kalk saturated water mixes into the tank and where the probe is located.

IMHO - I wouldn't trust a sensor to control/maintain the salinity in my tank. I think that you will be constantly adjusting minor fluctations in salinity either up or down. If your not careful, you may get a bouncing effect.

I also woudn't trust a cheap dosing pump. Thus, I'm prepared to spend the money for a high quality balanced pump setup.

[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?

[wolf_bluejay]

Originally Posted by abcha0s

However, the purpose of my post was to share my experience with salinity probes. They are increadibly sensative to stray voltages and tend to wander all over the place. Curt at Apex recommends that the salinity probe be placed in a drip cup to completely issolate it from the sytem. I was never able to get a consistant reading from my probe and basically threw it out.


IMHO - I wouldn't trust a sensor to control/maintain the salinity in my tank. I think that you will be constantly adjusting minor fluctations in salinity either up or down. If your not careful, you may get a bouncing effect.

I also woudn't trust a cheap dosing pump. Thus, I'm prepared to spend the money for a high quality balanced pump setup.

Grumble, grumble -- Ok, I have to admit, you are right on this -- a lot of the idea of using the controller really depends on getting a probe that accurately measures things. The delay in measurements is not a big deal as you could just have delays put into the pump cycle -- pump for a minute or 2 -- wait 10 -- check ph, repeat.

But I could see most of these probes being affected by stray voltage, calibration drift, and general crappiness that would cause the system to mess up the tank parameters big time.



Has anyone done the math on how much the salinity would be affected over time by not using "matched" pumps? If oyu have 200 gal tank, doing 2 gal a day water change, and the pumps are out by a bit --- how much would things get out of whack over the whole ~200 gal water change?

[sphelps]

You don't need to match pumps if you use a float, I posted an explanation earlier involving a slow fresh water top off and a fast saltwater top off. Using such a method will result in stable levels.

As for conductivity probes they do fluctuate in my experience as well but with the right controller you get use to quickly adjusting the calibration/set points on a weekly bases to maintain consistent salinity.

[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.