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Thread: Auto Water Change - Pros and Cons of Completing AWC in 2 Hours vs. 24 Hours

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    Auto Water Change - Pros and Cons of Completing AWC in 2 Hours vs. 24 Hours

    I just read through the Automatic Water Change instructions in the setup guide, and I actually understand them.

    The suggested program has the whole daily process completed in less than 2 hours.

    I was wondering: Why wouldn't I stretch this out over the course of 24 hours?

    My thinking is that making smaller changes over the course of a longer period of time would result in much less variation in my sump water level, with consequently in much less likelihood that my ATO system would be activated. I also imagine (though it's pure speculation) that there would be less stress on the pumps running at a lower speed over a longer period of time.

    Any thoughts?

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    I agree with you. I have my AWC change 20 gallons over the course of a week working 24 hours a day... I'm lucky because my DOS is in my basement and don't hear it. Some people might find the whine it makes annoying when it is quiet in the house so maybe they'd want to have it run over certain hours.

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    I have my DOS set up to change 1.5 gallons of water per day, and I use the "drain first then refill" approach. At 9:00am it begins draining out 1.5 gallons until 10:30am. At 10:30am, it then starts refilling 1.5 gallons until noon. During the whole process, I have my ATO disabled from 9am - noon so it doesn't try to refill with fresh water. The water level in my return chamber drops by about 3" but not enough to cause problems with my return pump, and the skimmer chamber level does not change. When the ATO finally resumes operation at noon, it typically runs for about 1.5 minutes to catch up on evaporation loss.

    I've had this set up and running daily for 4 months now, and it's been working flawlessly. I can't yet comment on DOS pump head wear & tear, but I have a couple of spare pump heads on hand if/when they start having problems.

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    Frequent Contributor zombie's Avatar
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    Unless you do drain then refill, slower is better. It allows changes to occur more gradually, which corals prefer and is less likely to be affected by ATO. I would consider pushing it out to 6 days a week 24 hours a day and refill on the 7th day for the most consistency.

    Sent from my SM-G965U using Tapatalk

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    The sound level is something to consider. I haven't installed the DOS units yet so I have no idea. I do know that my wife is ultra-sensitive to sound, so I'll be watching out for that.

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    My DOS is mounted on the wall in the garage where I have the mixing station set up. The aquarium is on the opposite side of that same wall in my living room, and I can definitely hear when the DOS is running. It would be quieter running at a slower speed, so if that's a big issue then slower is better. Where will your DOS be mounted?

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    I was internally arguing with myself about the drain-then-refill possibility.

    I was thinking that the simultaneous drain-and-refill method, displayed in the suggested DOS programing in the setup guide, wouldn't give as precise a percentage water change as might be expected because, with the see-sawing effect, the old saltwater being removed would not be "pure" old salt water but rather "diluted" by the new salt water. Then I realized that in the context of a 120 gallon tank (plus sump volume) the difference between the two methods is likely to be insignificant. There might be more of a significance if I were dealing with a nano setup.

    Given that thinking, I'm more inclined to go the simultaneous route so that my water levels remain relatively undisturbed.

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    I like your schedule. What total percentage of tank volume do you aim for over the course of your 6 days? 10%?

    I am nicely set up for this, with a large plastic reservoir from US Plastics (well over 40 gallons) that would let this process run for many days.

    With the AWC in place, do you (or anybody else) consider it advisable (or inadvisable) to do larger water changes periodically?

  9. #9
    Master Control Freak RussM's Avatar
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    Quote Originally Posted by rtolz View Post
    I was internally arguing with myself about the drain-then-refill possibility.

    I was thinking that the simultaneous drain-and-refill method, displayed in the suggested DOS programing in the setup guide, wouldn't give as precise a percentage water change as might be expected because, with the see-sawing effect, the old saltwater being removed would not be "pure" old salt water but rather "diluted" by the new salt water. Then I realized that in the context of a 120 gallon tank (plus sump volume) the difference between the two methods is likely to be insignificant.
    You are correct - the dilution factor is so small, it is insignificant. BTW, the AWC example in the DŌS manual is just that - an example. It's not necessarily a recommendation. On the other hand, the DŌS Get Started Guide (https://www.neptunesystems.com/getstarted/dos/) illustrates how to do continuous AWC over 24 hours, and this is the recommended approach for most.
    I'm not a Neptune support rep. Please do not send me PMs with technical questions or requesting assistance - use the forums for Apex help. PM me ONLY if the matter is of a private or personal nature. Thanks.

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    MY DOS will be mounted in the "laundry room" on the other side of the wall adjoining the tank. The tank is in the living/dining/kitchen area where we spend the majority of our waking time, so I don't want lots of added noises.

    Is there any difference between the DOS's sound levels depending on how many ML/MIN it's pushing?

    I already have a buzzy circulation pump on an Aqua-Maxx denitrator that I have to figure out how to silence or replace, and I don't want to add any more noise during waking hours.

  11. #11
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    Quote Originally Posted by rtolz View Post
    I was internally arguing with myself about the drain-then-refill possibility.

    I was thinking that the simultaneous drain-and-refill method, displayed in the suggested DOS programing in the setup guide, wouldn't give as precise a percentage water change as might be expected because, with the see-sawing effect, the old saltwater being removed would not be "pure" old salt water but rather "diluted" by the new salt water. Then I realized that in the context of a 120 gallon tank (plus sump volume) the difference between the two methods is likely to be insignificant. There might be more of a significance if I were dealing with a nano setup.

    Given that thinking, I'm more inclined to go the simultaneous route so that my water levels remain relatively undisturbed.
    A 30% continuous change is exactly equivalent to a 26% drain then fill water change from a nutrient export or addition standpoint. You trade a small amount of increased salt usage for a huge increase in consistency. RHF has a good write up that explains the intricate details.

    Sent from my SM-G965U using Tapatalk

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