I cannot recommend the Genesis Renew system (and Genesis ATO system, too) highly enough.
It uses a pair of metering buckets that are configured to deliver exactly one gallon of water to the aquarium or to remove one gallon of water from the aquarium. See attached photo. Each bucket has a standpipe inside of it. The height of the standpipe is set so that when water reaches the top of the standpipe, there is a gallon in the bucket. Excess water flows out the standpipe and back to the aquarium (e.g., the sump) from the one bucket, or back to the supply of new saltwater from the other bucket. The controller runs connected pumps – one in the sump, one connected to supply of new saltwater – long enough to guarantee the buckets are filled. (Float switch above the top of the standpipe will kill the pump if you fill too fast and exceed capacity of water to drain out the standpipe.) Once the buckets have been completely filled, a valve opens and the buckets drain. Old water goes to sink/drain, new water goes to aquarium.
As you look at the buckets in the photos, my sump is on the floor to the right, my supply of new saltwater is to the left. So, for the bucket on the left, supply of new saltwater is pumped to it via hose on the left, and standpipe drains and returns saltwater to the bin via the hose on the right. When bin is filled, it drains via fitting at the rear/center of the bucket, and the white pipe delivers it to the sump. For the bucket on the right, water from the sump is pumped into it via the hose on the left, and overflow from the bucket is returned to the sump via the hose on the right (which feeds it into the same white pipe). When the bucket is filled, the old water drains via the fitting at the rear/center, through that descending hose to a conduit that conveys it around the back left corner of the basement (on the left) and to the sink.
The buckets fill and drain simultaneously.
To prevent the ATO system from adding fresh water when the level drops in the sump as water is pulled from the sump for water change, the Renew controller and the ATO controller are connected via a cable and “talk” to each other, which disables the ATO controller when water change is taking place.
I have a level marker on the sump, and even after a 40-gallon change (which takes an hour or so), the level in the sump is spot-on. You tell the system how much of a water change you want to do (how many gallons) and whether that is daily, weekly, or continuous. If it’s continuous, the system turns on and runs continuously until it’s changed out the commanded amount.
The system runs 1 gallon out and 1 gallon in at a time. You don’t get the full benefit in terms of overall, actual change percentage of a water change of X% (e.g., if you set it to change 50 gallons on a 100 gallon system you haven’t really done a full 50% change), but it doesn’t shock the system and you don’t have to worry about matching temp since the new water will be dispersed and not affect temp by any noticeable amount. I haven’t run the math, but it’s close enough. Once it’s set up, it really is a GREAT system; I can’t recommend it highly enough.
(back when I had a 156 in my townhouse, RODI was in closet on lowest level, tank was on middle/main level. I’d mix 8 or 10 buckets of sw over course of several days (being careful not to overfill from the RODI outputting straight to buckets); drag them upstairs; fill 8 or ten additional buckets by siphon (trying not to spill); drag old to toilet and dump (again trying not to spill); dump new buckets in over time (trying to avoid shock); clean 16-20 buckets, and then look at my wife giving me the evil eye because I wasn’t spending family time…… those days are gone.
It really does work incredibly well, and well worth the money.
