How to do water change

[Notsolostfish]

Its my first sump system cycle ended. And i need to do my first water change. Its 18 gallon sump. I want to do 50%. The question is why people say mark your sump? Isnt when the water below the return pipe in the overflow box. The sump water line stays the same? Im confused.

 

[Gtinnel]

Before setting up an AWC I would turn my return pump off, siphon water from the display, and then fill back up to where water is at the same level (just where it would start running down into the sump).
I wouldn’t do the water change from the sump because it’s hard to siphon the water out assuming your sump is under the tank.

 

[Notsolostfish]

Before setting up an AWC I would turn my return pump off, siphon water from the display, and then fill back up to where water is at the same level (just where it would start running down into the sump).
I wouldn’t do the water change from the sump because it’s hard to siphon the water out assuming your sump is under the tank.

Yes i know that. Thats exactly my plan. But why people say u have to mark you sump waterline with a pen. If your sump water level wont change during the water change?

 

[Mark Goode]

I have a Brute bucket with freshly made saltwater, and I syphon from the DT into another Brute bucket to exactly the same level - then pump the new water back into the DT.

 

[Gtinnel]

Yes i know that. Thats exactly my plan. But why people say u have to mark you sump waterline with a pen. If your sump water level wont change during the water change?

The only reason I know of to mark the water level in a sump is so that you don’t overfill the system and overflow the sump when the return pump is shut off. I see no reason it would need marked for a water change.

 

[WallyTime7]

What Gtinnel said. If you mark your sump, you'll know what level is normal versus high/low. If mine falls below the mark, I may have an ATO clog if I moved it (sits above my sump) and if it's higher, I added too much water during my change. Which is fine, just have to calibrate my salinity to expect a slight bump with more saltwater.

 

[Notsolostfish]

Before setting up an AWC I would turn my return pump off, siphon water from the display, and then fill back up to where water is at the same level (just where it would start running down into the sump).
I wouldn’t do the water change from the sump because it’s hard to siphon the water out assuming your sump is under the tank.

So turn off the system. Syphon water out lets say 50% from display. And then fill back up where the water starts dropping to the sump and turn on the system?

 

[Gtinnel]

What Gtinnel said. If you mark your sump, you'll know what level is normal versus high/low. If mine falls below the mark, I may have an ATO clog if I moved it (sits above my sump) and if it's higher, I added too much water during my change. Which is fine, just have to calibrate my salinity to expect a slight bump with more saltwater.

Good point about marking the sump to make sure the ATO is functioning properly.

 

[Gtinnel]

So turn off the system. Syphon water out lets say 50% from display. And then fill back up where the water starts dropping to the sump and turn on the system?

Sounds correct to me. The only important thing is that you return the same amount of water that you take out. You can put a mark on the display tank to fill back up to, fill until just when it just starts going back into the sump, or pull out an amount of water equal to what you have to go back in like @Mark Goode mentioned. Whichever way works best for you is fine.

 

[Reab]

All good points here. Make sure your ato stays off for the entire process. The last thing you want is to have to deal with it dumping fresh water in as you get the level correct. I’m assuming people mark the sump so they can ensure they got the correct level. The chamber for the ato is much smaller than the display so you can get a better read on getting the exact amount in. Personally I don’t mark my sump but use my ato as my level.

my process. Turn off return, skimmer, heater, power heads, ato, any other pumps or reactors. Drain water from display for change. Pump water back into display until it goes down overflow, and then some as my wc pump isn’t as strong as my return(you’ll get a feel for the amount the more you do it) turn return on only, continue adding water until the level in the sump stabilizes to my “line”. Stop adding water and turn all pumps back on EXCEPT ATO. Top off back to the line for any water used by reactors or skimmer. Finally I will turn the ato back on.