[untamed]

Originally Posted by sphelps

If you want to keep a premixed salt storage tank then there is another fairly simple system you can employ.

• You essentially have two top off systems, one for fresh water and one for salt water.
• The fresh water top off works with a slow fill principal (slow pump or restricted solenoid valve).
• Saltwater top off works with a fast fill principal (large pump from storage container).
• Float switch for fresh water top off is located at standard height to maintain standard water level in sump. Should be controlled so water level remains fairly constant 24/7.
• Float switch for saltwater top off is located slightly below the float for fresh water.
• A pump on a timer pumps water out of the sump to a drain on a certain schedule to remove the desired amount of water.

Now the idea is the fresh water top off maintains the water level in the sump so the saltwater float isn't triggered from evaporation. However when the drain pump is activated the fresh water top off will be too slow to keep up so the salt flow will trigger and since it's fast fill, will top the tank back up before much fresh water is added. You'll also want to maintain the salinity of the storage tank slightly higher than the desired aquarium sanity as some extra fresh water will obviously be added every time saltwater is added.

I think that is pretty clever. You could add an additional, lower level, level sensor and only allow the fast SW fill cycle to initiate if BOTH the upper level AND lower level sensors are low. The only time that the lower level sensor would be low was during the extreme of a water change dump.

This gets around the problem of having the fast-fill trigger every time the sump even goes just a little bit low. It would wait until the sump is dramatically low.

An aquarium controller could handle that kind of logic. I know that Aquatronica could do it, and I assume that Profilux could also handle that.

In fact, while I've not rigged it to run automatically...what you describe is exactly what happens in my system during a water change. Even as I am refilling the WC sump with new SW, RO water is leaking slowing in because the main sump level is low. This extra top off water is insignificant in my system. In fact, because this is "extra" water added, the system returns to normal as this water evaporates away later. (that only works that way because I have 2 sumps)