Best Aquarium Hydrometers of 2025

"I needed to check the saline in my shrimp tank, and this hydrometer was easy to use and clean. Just remember to set it upside down on a flat surface to dry."

"After using a digital meter for a long time, I decided to test this hydrometer against it. It read a shocking 1.032g when the actual reading was 1.026g. I’m not sure if I got a defective one, but it really frustrated me, especially since it led to the loss of some of my corals."

"While I found the Coralife hydrometer to be a decent budget tool, I experienced some inconsistencies in readings. Sometimes it gave me two different measurements back-to-back, and I had to tap it to get a more accurate reading. I’ve since upgraded to a refractometer for better precision."

"I don't agree with the negative feedback. After getting it in my tank and removing the bubbles, it worked great! I topped off with RODI water, and I could see the salinity decrease on the gauge. It's a fantastic accessory for my tank."

"As a newcomer to the saltwater hobby, I find this product to be really effective. The readings are reliable, and I appreciate the suction cup feature. It's been a valuable tool for my mixing and maintaining routines, and I definitely recommend it!"

"I've had mixed results with the new units I ordered. Despite rinsing them thoroughly, I’ve encountered issues with air bubbles that prevent them from working as intended. My original one performed perfectly from day one, so I’m disappointed with this purchase."

"I needed this for a class study on salinity in Florida waterways. It worked beautifully, was easy to use, and transported easily. I love the quality of this product."

"I bought this thinking it would be super accurate. After calibrating with 35 ppm fluid and checking against other devices, it was off by 4 ppm. Still, I appreciate its functionality."

"I find this refractometer to be much easier and more accurate than the ones sold in pet stores. It has significantly improved my testing experience."

"My old refractometer was worn out, and I needed a replacement. This new one looks just like my old one and provides very accurate and reproducible results. I'm glad I bought it, but I recommend getting a fresh bottle of calibration fluid to ensure accuracy."

"I was a bit skeptical about the price, but I found this product to be extremely accurate. It's the same model my local aquarium store sells for $90. I would definitely recommend it for anyone with a saltwater tank!"

"Switching from a hydrometer to this tool was a game changer. It's quick, very accurate, and calibrates easily. Just remember to check it every few weeks or if you get an odd reading. Overall, for the price, it's a fantastic tool!"

"I used this to measure the salinity of my water for my brackish living fish. After watching a video on how to use it, I found it easy to operate. However, the numbers on the apparatus are small, making it hard for my child to read them accurately."

"I've been aiming for a salinity of 1.023, but my water tested at 1.030. I ended up getting another tester that points towards the light. Each salt mixes differently, and once I got my water down to 1.023, it registered 1.018 to 1.020 on this hygger's manual device."

"Having done marine aquariums for many years, I can say this tester is quick and accurate at a great price. I really appreciate how it simplifies the testing process."

"We use this tester to check the salinity of bayou water, which varies with the rain. It's simple to use: just fill it to the line and stir with the provided stick to avoid bubbles. The readings are easy to interpret, and I like that it shows specific gravity and conductivity as well."

"Before purchasing, I tried both a mechanical and an electronic salinity tester, and they provided significantly different readings for the same water sample. This product was the tie breaker. I found it much easier to use than expected, even with the high tannin levels in my water. It’s also well made and packaged."

"I have more confidence in this device than in my TDS meter with a salinity function. After calibrating it, I found it to be dead on accurate. Any distilled water I tested came out at exactly 0."

"For my two reef tanks, I depend on this for salinity accuracy, and it has consistently performed well for me. It hasn’t let me down yet!"

"I was excited to use this for my new saltwater aquarium, but I deeply regret purchasing it. The accuracy is so poor that I lost three $50 fish trying to get the salinity right. My readings showed .026, but the store said it was over .30. I tried diluting the water, and the tester only showed .20, but I ended up losing two more fish. I eventually bought a Coralife meter, which is incredibly accurate. To prove its inaccuracy, the store tested six of these meters, and not a single one was correct."

"I find it difficult to determine the true salinity level with this product. It's frustrating, as I expected better performance."

"I had high hopes for this, but it’s all over the place. I tested my aquarium multiple times and got readings like 1.015 and 1.035 from the same sample. It’s widely inaccurate and definitely not reliable for my reef or fowlr tank."

"As a newcomer, I made sure to follow the instructions carefully. Bubbles formed on the float, but shaking them off was easy. I wouldn’t recommend installing it in the tank due to potential algae growth. After a few tries, I got accurate readings, but I needed to check temperature conversions for my cold water fish."

"I’ve used several specific gravity meters over the years, but this Boxtech one has been surprisingly accurate compared to my refractometer. It reminds me of my first hydrometer from 30 years ago. Instant results are a huge advantage!"

"I bought this to help maintain the salinity for my brackish shrimp. Unfortunately, the readings seemed inconsistent; after adding salt, it showed varied results. I decided not to risk my shrimp’s health, so this meter is going straight to the trash."

"I was pleasantly surprised by how well this works. After calibrating it with a premixed fluid of known salinity, I found it easy to set up. Just be careful with the calibration screw; it feels quite delicate. Once set, it provides very accurate readings, although the glass quality is just okay. With decent light, it's readable."

"For the price I paid, I didn't expect much. When I checked it with RODI water, it showed 6 PPT, which was incorrect. After recalibrating it to zero, I tested it against a 35 PPT calibration solution and it matched perfectly. I hope it stays accurate!"

"I switched from a plastic hydrometer that was not accurate at all. This refractometer is super accurate and incredibly easy to use. I'm really happy with my purchase!"

"I've had my aquarium struggling for nearly six months, and I finally figured out that this device reads 20% lower than the actual value. It's a bit of a disappointment."

"While it works somewhat, I find it difficult to read. The longer I use it, the less accurate it seems to get."

"For about a year now, I've been using this device and it works great! I love that it can't go out of calibration and is set for salinity at 25°C, making it a useful calibration medium. My corals and fish seem to appreciate it."