how the auto water changer works!

auto topup kit - pro4

auto topup kit - pro4

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  • sensor cable length 40cm (designed to be positioned alongside the controller-we do not advise extending the cable length)

suitable up to 9mm glass/acrylic, clear or not clear

overseas shipping available

The ATU-PRO4 has all the same safety features of the ATU-PRO3 - the difference is in the sensor type, its outside the aquarium not in!

2 year sensor guarantee!

ATU4 is pre-wired and the unit is ready to use - includes:

  • The programmable controller
  • Supplied with sensor and mount
  • pump
  • A 2amp power supply
  • 2 metres small bore pipe w/hook outlet
  • full installation guide online


In a nutshell it shuts down the pump so the top-up is inoperative until you come along and reset it, indication that it has shut down is via the pump LED starts flashing and the alarm sounds for 30 seconds, sounder then repeats for 2 seconds at 15 minute intervals. Reset is a simple push of the button, once to silence the alarm and twice to full reset - if the cause of the fault is still present then it will go back into alarm state

 BONUS - Anti-Wave - many are familiar with the pump switching on and off every time you stick your hands in the water, or the same things happens if you have that powerful wave maker powerhead. This is addressed by a 3 second built in float delay activation, in other words the water level has to be "LOW" for 3 seconds before the pump starts, as soon as the level reaches a "HIGH" position the pump stops. The distance between high and low level is not measurable by conventional means the sensor is that accurate!

BONUS - Memory - that preset time you set up stays unless you reprogam, it is not lost on power failure!


  • sensor - capacitive
  • sensor cable length 40cm (designed to be positioned alongside the controller-we do not advise extending the cable length)
  • water level variance - less than 0.5mm
  • voltage - 12v DC
  • alarm - visual and audible programmable 5-60 seconds, pump auto cut-off on alarm
  • pump - 12v DC with up to 3m head height 
  • anti-wave - 3 second delay on pump activation
  • sensor mount - custom (exclusive)

    Customer Reviews

    Based on 3 reviews Write a review

    Customer Reviews

    Based on 6 reviews
    Keith Cross (Northampton, GB)
    Auto top up kit - pro4

    Purchased this as an updated redundancy item for my existing pro1kit with the Red Sea sensor. This old kit was purchased in early March 2017, still going strong and has never missed a beat apart from having to buy a replacement pump last year!
    The new pro4 looks extremely well made and has great features such as warning lights and alarms. I love the fact that the pump and hose have a good length of cable and pipe. This enables me to top up water from a separate 60Ltr barrel, instead of the tanks built in one. Especially useful when I am away from home. I am looking forward to using the Pro4 properly. It might be some time though because my original is still going strong!
    Many thanks Gordon, loving Reefloat products.

    Dominic Rigby (Aberdeen, GB)
    Great ATU

    I have always rated Gordons products, I have used his stuff since he first started, from AWC’s to ATU’s, he’s also helped me out numerous times at his own expense when I’ve needed quick fixes for other things or advise.

    This new ATU is great, got it installed in my sump, an although it’s tight (my sump) managed to calibrate the sensor just fine. It’s very well built an is made to last. Always loved reef floats stuff due to the built in alarm system, can’t fault that at all it’s a great feature. Thanks for making another great product Gordon 👍

    Gavin Candy (Beckenham, GB)
    Auto top up kit - pro 4

    I have had many auto top up systems on my tank. This is the only one that consistently work’s flawlessly.I cannot recommend this enough. Absolutely brilliant bit of kit. This is the 2nd one I have bought and the original did not come with the magnet to hold it on the sump. I spoke to reefloat and he sent me one out free of charge. Great service.

    James Cook
    Excellent product and customer service

    Can't praise this product enough, I had a TMC top off before and the float kept sticking, dumping all my ro into my tank. The atu4 sensor sits on the outside of your sump and works perfectly, I wasn't sure about a few things but the customer service is excellent and Gordon helped me whenever I needed it.

    J Almo
    Great ATU

    Genius piece of engineering. I saw this reviewed originally on the ReefDork channel and decided to give it a go. Not disappointed. The unit is discrete and accurate. Easy to setup, I really like the failsafes and alarm options. That impressed I’m looking at getting the auto water changer next.