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    • Controllers & Hydrometers

    Aquarium Controllers & Hydrometers

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    Best Selling

    See All- Best Selling
    • Milwaukee 716690 PH Controller
      Milwaukee 716690 PH Controller
      4.9 out of 5 stars (18)Total Ratings 18
      $130.00 New
    • Aquatek CO2 Mini Aquarium Regulator
      Aquatek CO2 Mini Aquarium Regulator
      4.5 out of 5 stars (95)Total Ratings 95
      $66.99 New
    • Neptune Systems EB832 Energy Bar
      Neptune Systems EB832 Energy Bar
      5 out of 5 stars (1)Total Ratings 1
      $313.14 New
    • Milwaukee MC720 PH Controller and Pump Kit
      Milwaukee MC720 PH Controller and Pump Kit
      4.3 out of 5 stars (12)Total Ratings 12
      $215.00 New
    • Neptune Systems Cor 20 Intelligent Return Pump
      Neptune Systems Cor 20 Intelligent Return Pump
      $369.99 New
    • Milwaukee Instruments Ph & ORP Controller Mc125
      Milwaukee Instruments Ph & ORP Controller Mc125
      $203.00 New
    • Seneye Reef Aquarium Monitor and Par Meter
      Seneye Reef Aquarium Monitor and Par Meter
      3.3 out of 5 stars (3)Total Ratings 3
      $219.00 New
      $140.00 Used
    • Aquatop Floating Glass Aquarium Thermometer W/ Suction Cup Mount
      Aquatop Floating Glass Aquarium Thermometer W/ Suction Cup Mount
      5 out of 5 stars (8)Total Ratings 8
      $4.64 New
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    2,258 Results

      • Unbranded
      • Neptune
      • Neptune Systems
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    • 1 Aquarium Fish Tank Thermometer Temp Sticker Stick on **FAHRENHEIT IN BOLD!**

      1 Aquarium Fish Tank Thermometer Temp Sticker Stick on **FAHRENHEIT IN BOLD!**

      $1.99
      4,193 sold
    • Aquarium Digital Thermometer Fish Tank Salt Water Terrarium with Extra Battery

      Aquarium Digital Thermometer Fish Tank Salt Water Terrarium with Extra Battery

      $5.98 to $17.89
      1,092 sold
    • One Aquarium Thermometer Temp Sticker  USA SELLER STICK ON!  🇺🇸

      One Aquarium Thermometer Temp Sticker USA SELLER STICK ON! 🇺🇸

      $1.99
      or Best Offer
    • AQUANEAT Aquarium Thermometer Digital Fish Tank Temperature 6 PCS

      AQUANEAT Aquarium Thermometer Digital Fish Tank Temperature 6 PCS

      $17.89
      3,468 sold
    • Neptune Apex Jr

      Neptune Apex Jr

      $95.00
      1 bid
      $20.00 shipping
      Ending Friday at 6:55PM PDT5d 10h
    • DIGITAL AQUATICS SYSTEM LAB 1 SL1

      DIGITAL AQUATICS SYSTEM LAB 1 SL1

      $9.99
      $2.50 shipping
      or Best Offer
    • Neptune Systems DDR DOS Dual Reservoir ( PLEASE READ)

      Neptune Systems DDR DOS Dual Reservoir ( PLEASE READ)

      $19.25
      0 bids
      $14.95 shipping
      Ending Friday at 10:18AM PDT5d 1h
    • 3X Aquarium LCD Digital Fish Thermometer Water Terrarium Black FREE Batteries

      3X Aquarium LCD Digital Fish Thermometer Water Terrarium Black FREE Batteries

      $9.68
      3,719 sold
    • AQUANEAT Aquarium Thermometer Digital Fish Tank Terrarium Water Temperature Test

      AQUANEAT Aquarium Thermometer Digital Fish Tank Terrarium Water Temperature Test

      $5.99
      743 sold
    • New Digital LCD Fish Tank Aquarium Marine Water Thermometer Temperature Black

      New Digital LCD Fish Tank Aquarium Marine Water Thermometer Temperature Black

      $6.29
      6,107 sold
    • Hanna Instruments HI772-26 Marine Alkalinity Checker Reagent 25 Tests ALK

      Hanna Instruments HI772-26 Marine Alkalinity Checker Reagent 25 Tests ALK

      $13.99
      478 sold
    • TUNZE 5000.020 REPLACEMENT ATO PUMP FOR 3155 OSMOLATOR 3152 NANO AUTO TOP OFF

      TUNZE 5000.020 REPLACEMENT ATO PUMP FOR 3155 OSMOLATOR 3152 NANO AUTO TOP OFF

      5 out of 5 stars (16)16 product ratings - TUNZE 5000.020 REPLACEMENT ATO PUMP FOR 3155 OSMOLATOR 3152 NANO AUTO TOP OFF
      $29.99
      505 sold
    • *NEW* AQUATEK Aquarium CO2 Regulator Mini with Integrated COOL TOUCH Solenoid

      *NEW* AQUATEK Aquarium CO2 Regulator Mini with Integrated COOL TOUCH Solenoid

      4.5 out of 5 stars (94)94 product ratings - *NEW* AQUATEK Aquarium CO2 Regulator Mini with Integrated COOL TOUCH Solenoid
      $66.99
      3,924 sold
    • New Digital LCD Fish Tank Aquarium Marine Water Thermometer Temperature Black
      SPONSORED

      New Digital LCD Fish Tank Aquarium Marine Water Thermometer Temperature Black

      4.5 out of 5 stars (49)49 product ratings - New Digital LCD Fish Tank Aquarium Marine Water Thermometer Temperature Black
      $6.59
      Was: $8.99
      Free shipping
      1,868 sold
    • Glass Thermometer Aquarium Fish Tank Water Temperature Meter With Suction Cup
      SPONSORED

      Glass Thermometer Aquarium Fish Tank Water Temperature Meter With Suction Cup

      $3.37
      Free shipping
      or Best Offer
    • Glass Thermometer Aquarium Fish Tank Water Temperature Meter Suction Cup Newly
      SPONSORED

      Glass Thermometer Aquarium Fish Tank Water Temperature Meter Suction Cup Newly

      $3.28
      Free shipping
      or Best Offer
    • DIGITAL AQUATICS REEFKEEPER LITE CONTROLLER

      DIGITAL AQUATICS REEFKEEPER LITE CONTROLLER

      $29.99
      $8.25 shipping
    • GrowBro CO2 Generator REFILL KIT Grow Box Cabinets Bucket Bag PC Hydroponic

      GrowBro CO2 Generator REFILL KIT Grow Box Cabinets Bucket Bag PC Hydroponic

      $15.99
      Free shipping
      or Best Offer
      519 sold
    • AQUANEAT Aquarium Thermometer Digital Fish Tank Temperature 3PCS

      AQUANEAT Aquarium Thermometer Digital Fish Tank Temperature 3PCS

      $10.35
      376 sold
    • Hanna Instruments HI758 Marine Calcium Checker Only Colorimeter (Saltwater)

      Hanna Instruments HI758 Marine Calcium Checker Only Colorimeter (Saltwater)

      $1.00
      1 bid
      $9.45 shipping
      Ending Saturday at 4:44PM PDT6d 8h
    • Duetto Dual-Sensor ATO Aquarium Auto-Top-Off System - XP Aqua

      Duetto Dual-Sensor ATO Aquarium Auto-Top-Off System - XP Aqua

      5 out of 5 stars (3)3 product ratings - Duetto Dual-Sensor ATO Aquarium Auto-Top-Off System - XP Aqua
      $89.95
      1 bid
      $20.25 shipping
      Ending Today at 9:10AM PDT44m 59s
    • Marina 11201  Floating Thermometer with Suction Cup

      Marina 11201 Floating Thermometer with Suction Cup

      4.5 out of 5 stars (4)4 product ratings - Marina 11201 Floating Thermometer with Suction Cup
      $8.85
    • DIGITAL AQUATICS REEFKEEPER BUS CABLES X3

      DIGITAL AQUATICS REEFKEEPER BUS CABLES X3

      $8.90
      0 bids
      $2.00 shipping
      Ending Saturday at 4:37PM PDT6d 8h
      or Best Offer
    • Apex Neptune Systems DOS Dosing and Fluid Metering System

      Apex Neptune Systems DOS Dosing and Fluid Metering System

      $228.50
      18 bids
      $13.90 shipping
      Ending Today at 5:45PM PDT9h 19m
    • Coralife Deep Six Hydrometer Wide-Range Specific Gravity Meter Accurate to 0.001

      Coralife Deep Six Hydrometer Wide-Range Specific Gravity Meter Accurate to 0.001

      4.5 out of 5 stars (14)14 product ratings - Coralife Deep Six Hydrometer Wide-Range Specific Gravity Meter Accurate to 0.001
      $12.64
      or Best Offer
    • Osmolator 3155 Auto Top Off - Tunze

      Osmolator 3155 Auto Top Off - Tunze

      $229.99
      321 sold
    • Used Neptune Apex EL Controller System

      Used Neptune Apex EL Controller System

      $400.00
      0 bids
      $11.75 shipping
      Ending Monday at 1:25PM PDT1d 4h
      or Best Offer
    • HANNA HI772 MARINE DKH ALKALINITY CHECKER HC ALK - HANNA INSTRUMENTS

      HANNA HI772 MARINE DKH ALKALINITY CHECKER HC ALK - HANNA INSTRUMENTS

      $54.49
      91 sold
    • 1-9PC Aquarium Digital Thermometer Fish Tank Terrarium Temperature with Battery
      SPONSORED

      1-9PC Aquarium Digital Thermometer Fish Tank Terrarium Temperature with Battery

      $5.99 to $29.99
      55 sold
    • BNC Electrode Probe Connector Hydroponic for PH Aquarium Controller Meter Sensor
      SPONSORED

      BNC Electrode Probe Connector Hydroponic for PH Aquarium Controller Meter Sensor

      $15.73
      Was: $17.48
      $1.00 shipping
      4 watching
    • Grow Bro CO2 Generator REFILL KIT  For Planted Aquariums organic bio co2
      SPONSORED

      Grow Bro CO2 Generator REFILL KIT For Planted Aquariums organic bio co2

      $15.99
      Free shipping
      or Best Offer
      421 sold
    • Guide for Trident Reagent Needle - Set of 3 - Reef Safe - APEX Neptune- 3D Print
      SPONSORED

      Guide for Trident Reagent Needle - Set of 3 - Reef Safe - APEX Neptune- 3D Print

      $6.49
      or Best Offer
    • Hanna Instruments Calcium Checker Reagent for 25 Tests HI758U-26

      Hanna Instruments Calcium Checker Reagent for 25 Tests HI758U-26

      $26.98
      99 sold
    • DDR Dual Reservoir - Neptune Systems

      DDR Dual Reservoir - Neptune Systems

      $76.00
      7 bids
      $13.15 shipping
      Ending Today at 5:45PM PDT9h 19m
    • DC24 Extension Wire For Neptune APEX

      DC24 Extension Wire For Neptune APEX

      $13.49
    •  CO2 Generator System For Planted Aquariums To 40 Gallons Organic Bio Safe

      CO2 Generator System For Planted Aquariums To 40 Gallons Organic Bio Safe

      $18.99
      Free shipping
      or Best Offer
      78 sold
    • HI713-25 Phosphate Low Range Checker Reagent (25 Tests) - Hanna Instruments

      HI713-25 Phosphate Low Range Checker Reagent (25 Tests) - Hanna Instruments

      $10.00
      $4.99 shipping
      Only 1 left!
    • Neptune Apex  Trident

      Neptune Apex  Trident

      $450.00
      $23.21 shipping
      or Best Offer
      17 watching
    • Waterproof LCD Digital Fish Tank Aquarium Thermometer Water Temperature Meter
      SPONSORED

      Waterproof LCD Digital Fish Tank Aquarium Thermometer Water Temperature Meter

      $9.03 to $9.13
      Was: $9.50
      Free shipping
    • Neptune Apex Trident, Source Tube and Waste Tube Organizers set of 4, 3D Printed
      SPONSORED

      Neptune Apex Trident, Source Tube and Waste Tube Organizers set of 4, 3D Printed

      $8.99
      Free shipping
    • JW Fusion Smart Temp Aquarium Thermometer

      JW Fusion Smart Temp Aquarium Thermometer

      $7.95
    • Aquarium Fish Tank Thermometer Temp Sticker Stick on **FAHRENHEIT IN BOLD!**

      Aquarium Fish Tank Thermometer Temp Sticker Stick on **FAHRENHEIT IN BOLD!**

      $1.99 to $4.99
      244 sold
    • 3D Apogee Par Sensor Wand

      3D Apogee Par Sensor Wand

      $22.00
      $5.15 shipping
      8 watching
    • Osmolator Nano 3152 Auto Top Off - Tunze

      Osmolator Nano 3152 Auto Top Off - Tunze

      $114.99
      164 sold
    • Neptune Systems  ATK - Automatic Top-off Kit - Used

      Neptune Systems ATK - Automatic Top-off Kit - Used

      $79.00
      0 bids
      $9.03 shipping
      Ending Friday at 9:00AM PDT5d
      or Best Offer
    • Aquatop Floating Glass Aquarium Thermometer w/ Suction Cup Mount  Free Shipping

      Aquatop Floating Glass Aquarium Thermometer w/ Suction Cup Mount Free Shipping

      5 out of 5 stars (8)8 product ratings - Aquatop Floating Glass Aquarium Thermometer w/ Suction Cup Mount Free Shipping
      $6.95
      302 sold
    • 1 EA  Dual Aquarium Fish Tank Thermometer Stick-on C*&F*C free ship fast ship

      1 EA Dual Aquarium Fish Tank Thermometer Stick-on C*&F*C free ship fast ship

      $2.23

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    Top Rated

    See All- Top Rated
    • Milwaukee 716690 PH Controller
      Milwaukee 716690 PH Controller
      4.9 out of 5 stars (18)Total Ratings 18
      87% agree - Would recommend
      $130.00 New
    • Zoo Med Digital Terrarium Thermometer Th24
      Zoo Med Digital Terrarium Thermometer Th24
      4.9 out of 5 stars (18)Total Ratings 18
      87% agree - Would recommend
      $9.00 New
    • Tunze USA 5000.020 Replacement Pump for Osmolator and Nano
      Tunze USA 5000.020 Replacement Pump for Osmolator and Nano
      4.8 out of 5 stars (16)Total Ratings 16
      90% agree - Would recommend
      $29.99 New
    • Milwaukee MW600 Polarographic Portable Dissolved Oxygen Meter
      Milwaukee MW600 Polarographic Portable Dissolved Oxygen Meter
      4.8 out of 5 stars (13)Total Ratings 13
      100% agree - Would recommend
      $189.41 New
    • Zoo Med Aquasun Aquarium Controller Timer & Power Strip White AA11
      Zoo Med Aquasun Aquarium Controller Timer & Power Strip White AA11
      4.8 out of 5 stars (13)Total Ratings 13
      100% agree - Would recommend
      $34.50 New
    • Cermedia MarinePure 1 5inch Sphere Biofilter Media for Marine and Freshwater
      Cermedia MarinePure 1 5inch Sphere Biofilter Media for Marine and Freshwater
      4.9 out of 5 stars (12)Total Ratings 12
      100% agree - Would recommend
      $28.89 New
    • Milwaukee MW102 Ph and Temperature Meter
      Milwaukee MW102 Ph and Temperature Meter
      4.8 out of 5 stars (11)Total Ratings 11
      100% agree - Would recommend
      $122.00 New
      $49.00 Used
    • Coralife 00232 Digital Thermometer
      Coralife 00232 Digital Thermometer
      5 out of 5 stars (10)Total Ratings 10
      100% agree - Would recommend
      $5.00 New
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