Automatic continuous water change

[Albertastorm]

Good Day fellow reefers!
Need some help.
I understand some reefers use a Neptune dose system to auto change water.
Equal volume waste water out equal volume new saltwater in.
And they also run an auto ROI water top off system to accommodate evaporation.
Why not just add more salt water back in at a lower salinity?
I'm just a simple Canadian farmer...but it seams to me to be a very simple calculation?
I have ran a Fresh water 5000 gallon winter Koi tank on this continuous water change principle for years and it seams to be the answer! No big water change all at once to drastically change water perameters.
Any simple monitoring system would alert you long before disaster of any up coming problems?
Any normal sump would show you any slight differences in the differences from in to out water volumes.
Why are more people not doing this?... it is so easy and trouble free?
I'm missing something

 

[mcarroll]

I think it's up front costs combined with lack of familiarity.

A bucket and hose for traditional, well-understood water changes costs around $5.

An auto-change system probably costs 10x-50x that, or even significantly more.

 

[andrew james]

I do this using a DOS. I continually change water in my system 13l per day. I've also setup a program to quickly change out water for emergencies it will do about 15l per hour at its fastest. I also use a DOS to do ATO but I run it from my fresh water storage rather than my RO system. This way the RO system stays off and I dont produce as much waste. I also use several floats to guard against overflow and have a one of my DOS pump out extra water if the sump is too full.

It took me a minute to get it setup correctly. I dont want my ATO running while my water change is running because that can mess up parameters but after that I got it all worked out I dont think I'll ever own a tank again without it.

 

[Albertastorm]

Thanks for the input.
But I was thinking of the people that have the equipment and are doing both now.
Why not just lower the salinity and use one dose system?

 

[andrew james]

If you could control evaporation perfectly and where really good at math it would work that way.

 

[sinekal]

I think it's possible, take some saltwater out, and have the top off that is already occurring replace it by adjusting the salinity of the top off water. I think the challenge compared to an auto water change that's separate from the auto top off would be the need to continually adjust the amount of salt you add to adjust for seasonal changes in evaporation.