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Barrel Tender V2
Barrel Tender V2
Barrel Tender V2

Barrel Tender V2

$ 209.99

The Barrel Tender is a unique device designed to automatically regulate reverse osmosis (RO) water production and greatly reduce the negative effects of TDS creep.  The Tender senses when the RO reservoir is nearly empty, then turns on the RO system until the reservoir is full.  This allows the RO unit to run for longer periods of time, which maximizes filter efficiency.  

New Features

New for the V2 Tender is a Neptune Apex and GHL Profilux aquarium controller integrated version, which allows you monitor and fine tune RO water production.  The aquarium controller version does require an Apex or Profilux controller and a break out box or input board, respectively.  We have several break out box options here. Also, the new housing design incorporates a super bright edge-lit acrylic top, so you can see when it is active even when tucked away in the corner of your basement.  Lastly, we upgraded several key components and made it even easier to install.  



Reverse Osmosis water reservoirs are conventionally difficult to keep full on a regular basis due to the need to manually turn the system on and then remembering to turn it off hours or even days later.  Larger remote vessels can run dry due to "out of sight, out of mind" circumstances, resulting in having no water when you need it.  We have even heard of people using timers, keeping their RO reservoir in a bathtub to prevent floods caused from forgetting to turn the system off, and other wacky solutions that lead to frustrations with aquarium keeping.  The Tender is a set it and forget it solution for top off water production.


TDS (Total Dissolved Solids) creep occurs when previously removed pollutants on one side of the RO membrane leach across into leftover water on the "clean" side.  When the RO unit is restarted, these pollutants are washed out with the first little bit of "good" water.  If you are using a Deionization (DI) postfilter, the DI resin then absorbs this little blast of pollutants, but the result is that the DI resin is exhausted faster.  Otherwise, the pollutants go into your aquarium.  You get this little pollutant blast every time the system switches on, even when using an autoflushing system.  Running an RO unit for just a few ounces of water at a time, e.g., each time your top-off pump turns on and opens a float valve, means you are effectively losing the benefit of the RO membrane.  Conversely, If your RO system is allowed to run for longer periods of time, that initial pollutant blast is largely diluted by the large volume of clean water that follows.  If you are using a DI postfilter, this means the DI resin only has to pull out the initial pollutants once for a large volume of water, rather than many times over each small on/off cycle.  The bottom line is you'll save a lot of money on DI resin replacement.


Footprint: 6" x 4.5" 
Height: 5"

Power: 12v 

Rated for booster pumps up to 135 PSI.  Requires an Auto Shut Off Valve (ASOV) on RODI unit.  The Apex version requires a Neptune Apex controller and a Break out Box

Using the Barrel Tender with a GHL Profilux requires a PLM-ADIN add-on board, and a db9 terminal adapter.  See this thread on for more details.

What's included:

Barrel Tender with your choice of control and plug type along with all the tubing, fittings and nuts and bolts to install on barrels up to 32" deep along with a drilling template. Extra rigid tubing for deeper water reservoirs is available here.

See this template for dimensions required for installation.  We include a cardboard version of this in the box for installation convenience.


Apex version installation and programming instructions


Customer Reviews

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Very Happy

Install was easy enough. Glad to finally have my water making and ATO now fully automized.

Jason L.
United States

Easy install, great product

1 leak/overflow is too many: with this product, attached to my apex, I have peace of mind

Matt S.
United States

Awesome automatic option

Super easy to install with included template for barrel lid. Up and running in 15 minutes, haven't looked back. Keep up the good work Avast!

Kim J.
United States

Love it

I love this thing and as always great customer service from avast marine

Ryan S

Time control over production, cheaper then Apex accessories.

Outstanding piece of mine and efficiency in a single unit, better then any Apex module and way cheaper. I have this hooked up in a room 42' from my Apex. Running a simple power cord and one cheap cat 5/6 multi wire I was able to set up a leak detector and control my water production with confidence. I didn't need to buy a bunch of extra Apex modules or expensive cords, and costly accessories for an Apex as with other units. I also didn't need a degree to figure it out... it's all here. Since I use a booster pump I ran a final float valve just as a last resort but I believe the solenoid switch is designed to fail closed. Lastly, as a personal paranoia from past incidents I set my Apex to only allow production during specific hours so that I know I'm normally around... AND I CAN'T FORGET I LEFT IT ON!