Sump level after water changes

[hannernanner]

Hi all! My first reef tank has been set up for about a month now, and I've done 2 water changes thus far. My issue is that after I do the water change, I seem to be endlessly fiddling with the ATO sensor and gate valve to get the sump water level right where it was before. This part seems to take longer than the water change itself! I mark the "Run" and "Max" water levels in my sump, and when I add water back to the tank (return pump off) I fill it to the "Max" line and turn the pump back on. Then I wait a while and turn the ATO back on. No matter what the ATO always kicks on when I turn it back on, so I'm always moving the sensor so it stops. After a water change this weekend, I thought I had everything running right and then my ATO dumped way too much freshwater in overnight, and now my sump level is far too high. I don't know how this happened. For now I just readjusted the ATO and I'm going to remove some water. Any tips/tricks to do this more efficiently? It's driving me nuts!

 

[ReefRusty]

My tank does the same but even when I turn the return pump off for a minute then back on its never the same as before, have to adjust pump speed to allow water to drain down pipe before setting it back to the normal setting, and sometimes evwn adjusting the ball valve. Does my head in.

 

[Reefer508]

Whenever I turn power back on to ATO systems they will turn on the pump. What I started doing is to remove the sensor from the reservoir so the system thinks it's empty. Then put it back in after WC so I don't get that freshwater dump.

 

[hannernanner]

Whenever I turn power back on to ATO systems they will turn on the pump. What I started doing is to remove the sensor from the reservoir so the system thinks it's empty. Then put it back in after WC so I don't get that freshwater dump.

That would be a good solution, although unless I’ve missed something the Tunze I’m using doesn’t have a reservoir sensor.

 

[fishybizzness]

Hi. The tunze ato will always kick on when you turn it on. The water added is very minimal and changes to salinity is insignificant and will stabilize in the sump after a little water evaporates. If your tank is smaller than around 40-45 gallons the nano ato is a better choice as it does not have that auto add feature as the larger one does. The only way that the ato would keep adding water after the initial small amount is if the sensor is dirty/has buildup on it. When i do my water changes, i have a container marked with 5 gallon and 10 gallon levels, depends on which tank I'm working on. I shut off the pumps and all flow and wait for everything to level off. I then take a small piece of masking tape and mark the level to know where to refill to as i have a 50 gallon saltwater holding bin. I then siphon off how much water I'm going to change, refill with new saltwater to the tape line and turn everything back on. takes about 10 minutes max and i know I'm adding exactly how much i removed. I also have a running level marked on the sump return section. When i see the water stabilized at the mark on the sump return section i then turn on the ato and done. Hope this helps.

 

[SPR1968]

As said above its worth adding a marker to the sump so you know exactly how much water to put back in.

As far as the Tunze, if its the Osmolator it has a turn switch inside the unit that you can turn down for smaller tanks so that might help out as well.

You could also under fill the sump slightly to take into account when you turn the ATO back on as another option

 

[Joe31415]

I'm very new to all this but a few things I've noticed are that, for starters, if you had your siphon set up just right, it'll get back to where it was before. It might take a minute (or 2 or 10) to get all the air worked out and everything leveled off, but it'll get there. I always kick myself when I start messing with the valve to get the siphon started. As soon as I do that, I know I'm going to be spending the next 10 minutes trying to get it back to where it was.
I have found that sometimes instead messing with the valve to get it going, I can put my fingers on the overflow to force more through the siphon, just have to be careful the box doesn't overflow.

Second, at least for me, the height of the water in the pump section of the set up seems to change how fast the water gets pumped up. When the water is running low, everything is fine, when it's an inch or two higher, I can hear it trickling through the overflow drain. I assume that, at least with my system, everything is balanced in such a way that the higher water level (even an inch or two) means there's just slightly less head pressure on the pump and it can move slightly more water, hence it hitting the overflow. I adjusted my ATO sensor so that doesn't happen.

 

[ReefPig]

I just turn off my ATO when doing a water change, and I've mark on the sump to the correct level.
Never been an issue doing water changes like this.

 

[Joe31415]

You could also under fill the sump slightly to take into account when you turn the ATO back on as another option

It would have to be very slightly or you'd risk dropping your salinity.

 

[Ippyroy]

It is putting in such a small amount of water that it shouldn't have any negative affects. Next time you do a WC, catch the water and measure it. You are MLs not OZs. If you are worried, simply test the salinity 30 minutes after the ATO shuts off.

 

[uninformed]

Second, at least for me, the height of the water in the pump section of the set up seems to change how fast the water gets pumped up. When the water is running low, everything is fine, when it's an inch or two higher,

It's an academic point, but for the purposes of helping others understand how centrifugal pumps work, the higher water level in the return chamber increases the head pressure on the suction side of the pump. You can think of it a couple different ways, but essentially, the pump imparts a fixed amount of energy into the water as pressure, so the more pressure you provide on the suction side, the more pressure you get on the discharge side, and therefore higher flow.

 

[Joe31415]

But shouldn't increased head pressure on the suction side mean the pump doesn't have to work as hard since the extra height/weight of the water column is doing some of the work? Plus, if the water is higher, that's going to reduce the head pressure on the discharged side of the pump.

Wait, maybe we're on the same page. Were you agreeing or disagreeing with me?

 

[Joe31415]

It is putting in such a small amount of water that it shouldn't have any negative affects. Next time you do a WC, catch the water and measure it. You are MLs not OZs. If you are worried, simply test the salinity 30 minutes after the ATO shuts off.

I agree, I just figured it's a point worth noting. If you're putting in MLs, it's not going to change it by more than how much it changes just due to evaporation and topping off. It's just something to keep in the back of your mind.

 

[uninformed]

But shouldn't increased head pressure on the suction side mean the pump doesn't have to work as hard since the extra height/weight of the water column is doing some of the work? Plus, if the water is higher, that's going to reduce the head pressure on the discharged side of the pump.

Wait, maybe we're on the same page. Were you agreeing or disagreeing with me?

I certainly wasn't trying to establish sides...LOL...just making sure you know it works. I read a lot of misconceptions here about pumps and pumping and sump levels.

The simple way to think about it, which is where I think you were going, is in terms of "net head pressure." If you have 5 feet from your pump to the outlet in your tank, but only run in 6 inches of water, you have 4.5 feet of net head to overcome. However, if you run in 1 foot of water, you only have 4 feet of net head to overcome and the pump will move more water.

For the more technical discussion:

Your observation was right about the water level and flow, but the pump doesn't "know" how hard it has to work. The motor spins the impeller and imparts a fixed amount of energy to the fluid as pressure, flow (kinetic energy), and heat (friction). In most cases, that energy results an fixed increase in pressure from one side of the pump to the other. Therefore, when you increase the pressure on the suction side, you get a higher pressure on the discharge side.

The flow rate of water is a function of the pump discharge pressure less (1) the pressure at the other end of the pipe, (2) the static "head" pressure (i.e. the vertical distance from the pump discharge in your sump to the outlet in the tank), and (3) the frictional losses due to the piping and fittings. Now consider our reef tanks, where the pressure at the outlet of the pipe (1) is essentially 0 PSIG, the static head pressure (2) doesn't change, and frictional losses (3) are much, much smaller than the static head pressure (and a function of the flow rate itself). Any increase in suction side pressure will result in an equivalent increase in discharge side pressure, and therefore, an increase in flow. The higher pressure on one side of the pipe "pushes" the water through the pipe faster.

Source: I was a chemical engineer once upon a time.