I hope I've followed your original description of this system properly, but it sounds like you will first pump in a bunch of fresh water to the sump, and then gradually return the water to the correct salinity using the super saturated solution. Is that right?

would that kill stuff living on live rock you have in the sump?

What about a more cartridge like system
 

The original idea about this came from a sampling system for ocean water at different depth -- so pardon me if the idea sounds half baked.


Why bother with a hopper or motor controlled device that can cause problems -- why not have multiple "drops" of measured salt.

In the most simple but costly version: have 5-10 pvc tubes sealed on top with a flapper on the bottom controlled by a small motor each. Into each one goes to correct amount of salt for the mixing tank and all are placed above the tank. For a batch of salt, add water, open 1 tube, mix and serve.

On the cheap you could do a circle of tubes with flappers and a disk on the bottom with 1 hole in it. rotate disk a little and 1 tube opens through the hole.

A little less automatic for a whole bucket of salt, but would work well for 5,10,20 batches that you could measure out all at once and forget it.

Pretty much, when water is removed from the sump the controller will continuously switch between fresh water and saturated salt water top offs to control salinity with the aquarium until the sump water level is restored. The top off flow rates are typically pretty low compared to the sump turnover rate so there should never be any large spikes of high or low salinity to affect anything in the sump or display. There's really no difference between this and a regular top off. A regular fresh water top off adds fresh water directly to the sump and it doesn't effect anything. Adding the saturated salt water will be the same.

You should however have the two water inputs upstream in the sump from the salinity probe otherwise the reaction time for adjustment may be too slow and you'll end up with a bigger range in salinity.

Also so if anyone else is interested in another alternative to auto water change without a salinity probe you could setup something like this:

• Two separate top offs will be needed, one for fresh and one for salt.
• The fresh water top off is simply just your standard fresh water top off, set the float switch to trigger at your desired sump level. The only difference is you want the fresh water to be added slowly so use a small pump or restricted pressure/gravity feed.
• The saltwater top off will require a decent size storage tank where you can store premixed saltwater (the same salinity as the display). Install a separate float for the saltwater top off slightly lower than the fresh water float. Just low enough so the saltwater float isn’t triggered from evaporation.
• The saltwater top off should have a fast flow rate so use a decent sized pump.
• Next install another decent sized pump in the sump to remove water quickly for water changes. You can use a timer to activate it or just a switch if you prefer to keep more manual control over the system.

That’s pretty much it. The fresh water top off will replace evaporated water, the slower flow rate will keep up evaporation since this is a slow process. When the pump in the sump is activated to remove water it will do so quickly and activate the lower float switch which will trigger the salt top off. Since the fresh water flow rate is slow the fast saltwater flow rate will top off removed water before much fresh water is added. To make up for the small amount of extra fresh water added during a water change to can keep your salinity a little higher in your make up container. How much higher will depend on your setup and may require a little experimenting.

To limit the size of the container you need for saltwater storage you can try using saturated salt water. You will have to experiment but by placing the saltwater float lower in the sump you can control how much saturated solution is added in comparison to fresh water. You will however have to maintain a constant salinity in the make up container. You can either maintain a high salinity by measuring or you can maintain maximum saturation by keeping temperature consistent and always making sure some salt remains undissolved

Curious as to why you leave some undissolved?

I agree that supersaturation is the solution to an economical top off design but a number of questions have been raised and it would be interesting to understand how many of the questions are valid, usually we mix batches of salt well ahead of when we do changes, some say this is needed to allow all chemicals to mix thoroughly,can we take a cup of salt, mix and serve immediately with no adverse effects?


Liquid handling isn't rocket science, I use proportionalizer valves every day and they work fine, precipitation is another issue in premixes as I am told, which could lead to other problems, removing a known amount daily and replacing the same volume appears to be less constructive as doing larger batches fewer times... true false?

speaking of liquid handling.......http://www.wimp.com/beerscup/

Automation can be a good thing, but for mixing your salt water? Come on, such a simple task and we try to complicate it by coming up with some ingenious, but quite technical and work intensive/costly ideas. How long does it take to measure some salt, toss it into your mixing container and give it a stir or start up a powerhead? Augers, valves, proportionizers..... egad. The maintenance of all the extra gear sounds like more work to me than just doing it manually. Apologies if I sound a little negative here, not really my intent, just trying to present the simpler point of view.

I just use the highly advanced method of drawing a line inside a bucket, filling the water to the line and writing on the outside of the bucket how much salt is required to bring that volume of water to the desired salinity. Works every time and takes about 30 seconds a week to make up my water change water. No extra cost or maintenance. Nothing at all wrong with mechanizing things but its up to the individual to determine if it is really saving any time or effort.

Do you have a rotary phone?

Seen one for sale lately?

Ensuring some salt always remains undissolved insures the salt solution is at max saturation and with constant temperature you can be sure the the salinity of the make up is consistent (max saturation at given temp). You could also in theory measure the salinity and keep it constant however it can be difficult to measure salinity of saturated saltwater and it's easier to just simply look for undissolved salt. It makes other options easier to employ as well. This is of course only important without the use of controllers, a controller eliminates the need to maintain constant salinity in make up water.

Some salts seem to require longer mixing times but I've used many salts that mix clear almost immediately and I've added cups of salt directly to sumps many times while preforming water changes without any adverse effects. Other peoples results may vary but I've never really pre-mixed saltwater ahead more than a few hours or so, typically I mix new water at the same time as I'm removing old water.

In the automated systems I've used and setup in the past I've always put importance on the less more often approach for stability. The systems would usually change a smaller percentage daily rather than a larger amount weekly or even monthly. This could very well be an important part of the systems I've previously described.