I had a love/hate relationship with this vac for 1.5 years. I just bought my 2nd one 6 mos. ago and I learned a lot in that time period. It is the best vacuum of its kind. Many of us don’t want to take a large amount of water out of the tank as a result of vacuuming it. I have a single goldfish in a 40-gallon breeder tank, and I’m amazed at how much crap comes out of that fish. I need to vacuum almost daily, but don’t need to change the water that frequently. Plus, it takes me a long time to vacuum, so if I used a siphon all the water would be long gone before I finished. This vac solves that problem nicely. It can either save you time or cause you huge amounts of stress, depending on how you use it. The picture above shows my tank with its original sand substrate (I chose it because everyone said it would be “easier to clean”). It was a nightmare. It looked pretty but it was actually harder to clean for me because all the detritus, bacteria, and funk stuck to it. It would form a little crappy sand ball and would become too heavy to suck up. I would literally stand there and curse at the vacuum after an hour of cleaning was still unfinished. I hated it but needed it! Eheim recommends NOT using this vac on a fine-grained substrate. I thought I was smarter than that and did it anyway. Bad idea. Sand will eventually destroy the vac and cause it to work terribly until the point that it eventually dies. Sand and other similarly fine-grained substrates will rub against the magnetic impeller/shaft and wear the metal away. I learned this the hard way. If you use the extension tube to put distance between the substrate and the impeller, it loses the strength of suction and becomes useless. I think it works great with just one tube, but not 2. That’s why I’m not sure this vac would work well on deeper tanks that would require that extra tubing length to reach the bottom without submerging the battery compartment. My tank is about 17” deep when full. I take out some water before starting, so it’s about 13”-14” deep when I vacuum. That will cover the mesh holding compartment and just reach the bottom of the handle. It’s okay to get the bottom of the handle wet, but stop before it reaches your hand. It works best when the whole mesh area is submerged. I also learned this the hard way. I don’t want to tempt fate, but I have never had a problem with water getting into the battery compartment. I make sure the cap is pushed down/sealed tightly before starting and never get that portion wet. Any water entering that area would corrode the wires inside. I removed all my sand substrate 6 mos ago and then started with a new Eheim vac. Amazingly, when I follow the manufacturer’s instructions, it works perfectly! It was the sand, not the vacuum that was the problem all along. Make sure you buy good quality 1.5v rechargeable batteries at the same time you buy the vac. I recharge mine about every 4th session. Don’t be worried about negative reviews on this product. I would have given it 1-star last year. Just reduce your water depth to about 14” before vacuuming, don’t use on a fine-grained substrate, make sure your 1.5v batteries are charged and you should be fine. A little patience may be required.