I have a 90 gallon container that i mix every month. I have my apex dos set up to do a 10% water change every week. I spread it out over 7 days of course but i mix my salt ahead of time. If your doing a huge water change then of course youll want the temp to match along with salinity.
Since im only changing 3 gallons a day i dont preheat the water prior to my water changes. I do preheat the water when i mix it though. Its easier to mix the salt and then i turn my heaters off. I dont think changing out 3g over 2 hours is enough to make a difference in a 210g system. I do make sure the salinity matches though with the cond probe in the container. I havent had any issues with it yet.
I do have an ice cap gyre in my container that is constantly mixing the water so it doesnt sit. No air, just mixing. I have my apex set to turn that pump on every hour for 5min to keep the water moving. I had to install a pump in the salt container because i was getting a white salt film on the walls of my container from all the mixing if i let it sit there. I cleaned it up and installed the gyre and no problems since. I have a sideways tank, not tall so the gyre is turning the water in circles and it gets plenty of air contact on the top. the waters always moving.
This is what I did. I got the acrylic ro/di tube from brs and the bulk head so its a stiff line going down to an exact measurement in my container. I have the apex sensors that let me know when my container is low and need to add more water. I ended up getting the pmup pump that i installed into my ro container and its configured to fill my salt container back to the top with ro/di water when it gets low to a certain level and activates the sensor. Since i have a hard 1/4 tube going into my container I’ve timed it so that apex will let me know when im low and it will automatically fill my salt container up with ro/di and let me know once its full. Then ive calculated exacty how much salt to add so that when the apex alerts me that im low, it will automatically fill the container back up, alert me that its ready for salt, i pour the pre-measured amount of salt in and it gets me pretty darn close to where i need to be. I created a virtual outlet that i trigger after pouring the salt in that will run the gyre for the next 8 hours mixing it throughly, but after that, i l leave it alone and it mixes alone, then does all the daily water changes alone, and just lets me know next time it needs me to pour salt in.
I have a sensor in my ro/di unit as well and tell my apex to ALWAYS have my container filled to that line. Sometimes at night ill hear my ATO kick on and secondly after ill hear the water valve open where the apex is making more ro/di water to always have that container at the 90g mark of ro water. I love the apex, theres so much you can do if you get creative.
