Why Choose Ultimate ATO?
With 2 X dual-optical sensors, the Ultimate ATO is the first ATO to include 4 sensors. The 4 sensors allow us to design a dual-stage overfill alarm that is less intrusive as well as a run-dry protection feature that prevents your sump from running dry: which is also a first. The Ultimate ATO’s versatility is also unmatched. An efficient DC pump is included for a standard installation. If you require a larger ATO pump for a remote sump installation, a Socket Switch is included that allows you to run a pump up to 10A (1000W). A solenoid valve is also included for aquariums that are topped off directly with an RO/DI system. We designed the Ultimate ATO to offer you the ultimate protection with the ultimate convenience!
*Please avoid setting up the sensor in an area with micro bubbles or direct light.
Ever since the ATO systems were invented by Tunze in 1985, they have been helping saltwater reef aquarium hobbyists maintain stable salinity levels and offering a ton of convenience. ATO is short for ‘aquarium top off’ system. It is also called an ATK ‘aquarium top-off kit’, or osmolator / osmo regulator in Europe. Here at XP Aqua, we have combined all the best ATO technologies and added several proprietary features to create the safest and most dependable ATO money can buy! Our micro sized ATO sensor features two precise optical sensors to offer you more protection. Additionally, each XP Aqua ATO system includes our intelligent QST programming to prevent overflows. If you are looking for the best ATO system, check out our awesome line of ATOs!
Most orders under $39 ship for only $5.99 using a mix of economy shipping methods including UPS Ground, USPS First Class, and/or SurePost. Your order will be delivered in up to 7 business days after it ships out.
We ship 99% of the products we carry for free within the contiguous United States using a mix of economy methods including USPS First Class Mail, SurePost and UPS Ground. Your order will arrive in up to 7 business days. Just spend $39 or more!
Over 90% of shoppers receive their orders within 1-2 business days. Upgrade from free economy shipping to faster shipping for only $5.99—or spend $250 and we'll upgrade you automatically!
Expedited shipping services are available for most products if you are in a hurry. Get guaranteed delivery in 2 business days, 1 business day, or next day by 10:30 am. Costs vary by location.
Same-day shipping is available Monday-Friday for most products—place your order by 10:30 am PST. Pre-ordered and back-ordered items do not qualify, nor do drop-shipped, live, or frozen shipments.
We ship live plants, live foods, and frozen foods within the contiguous United States. Each of these categories is subject to its own $19.99 flat-rate shipping fee to cover the special packaging and/or expedited shipping costs required to ensure safe delivery. Orders with 12+ live plants ship free!
Return any new and unused item within 60 days for a full refund. Having difficulty with a product? Contact us to speak with an aquarium expert. If you need a replacement, fill out this form.
A small segment of the 180+ brands we carry require that customers contact them directly if/when problems arise. You can view the full list of those brands and get their contact info here.
We are unable to accept returns of Digital Aquatics, Neptune Systems, Vertex Aquaristik, Aqua Illumination (AI), EcoTech Marine, GHL, or Seneye products once the manufacturer's packaging seals have been broken.
Marine Depot is an authorized reseller for every product we carry. That means when you buy aquarium supplies from us, your products are not only backed by our own 60-day return policy, they also carry full factory warranties, where applicable. Some items have a 1-year warranty, others have limited lifetime warranties. Warranty coverage varies from manufacturer to manufacturer, so please read the product description of the item(s) you are considering thoroughly for details or contact us if you have warranty questions.
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