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Old 11/10/2005, 11:37 PM
Anthony Calfo Anthony Calfo is offline
Parapterois heterura
 
Join Date: Nov 2001
Location: Pennsylvania
Posts: 5,141
its rather easy...

you have your evap top off device set wherever you want/need the water level in the sump proper (last and lowest sump compartment).

Set the evap float swithc so that it is very finely sensitive (frequently doses small amounts) but is fed by a VERY slow pump (extreme here... 1/4" airline or icemaker line style stream... mere gallons per day rate of speed)

Then you have your auto water change overflow hole drilled either a) slightly higher than the evap-top off level by say... not more than 1/2", or b) drilled at the same level as the evap top off level but with an adjustable elbow that allows you to change the overflow level (my recommendation)

Thus... with the overflow hole/height being less than half inch over the evap-top off level... you can auto (timer) pump new and slightly cooler seawater (no more than 2F cooler) into the display tank which will displace warmer aged water to the sump and out/over the overflow hole! Automatic water change.

And from a waiting/reserve vat (barrel/buckets... whatever) of new seawater... your auto-timer (digital from Radio Shack, for example) can be programmed to do daily, weekly, etc water changes as you wish! Sit down once and calculate how many gallons per day/week you want to change... and how many gallons per minute the pump you use for make-up will push. Simple math.

Then... after just a little bit of evaporation (after each auto water change that bullrushes the sump and overflow hole) the sump proper resumes normal evap top off operations in wait for next auto-water change, which will again slightly overun the evap top off level by just 1/2" or less

Now you may be wondering... isn't that slight overun (<1/2" over float switch level) adding a little bit of salt to the tank and increasing my salinity slowly over time? Well... theoretically yes. But if you will worry about that, then are you also calculating the similarly lost salt due to salt creep? Heehe... point is, either way its a small amount of salt. And either way, with or without salt added or exported (creep)... you still need to make slight corrections over time to the tank by checking salinity. If its a big deal (large sump)... you can compensate then by making your new seawater used for auto-water changes just slightly less saline.

And voila... automatic water changes!
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