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As far as gravel cleaners go, there is no unbelievable advantage of the hydrocleans compared to any other gravel cleaner. The hydrocleans have a supposed unique starting mechanism, using a shaking movement, and a non return valve in the unit itself. Although this method does work, it is a lot more fiddly than simply sucking the end of the pipe to get a syphon going. All that said, when the syphon is going, there are an efficient gravel cleaner. They have a useful shaped tube that is straight on two sides, creating a perfect corner, allowing you to obviously get right into the corner of your tank. They also have a little tap at the top of the yellow tube, allowing you to stop the syphon, without actually losing the syphon. This is particularly useful if you need to go and empty your bucket, Saves you having to suck the pipe all over again when you return.
This is a product which is supposed to clean the muck out of the gravel in your fish tank. They are basically a glorified syphon which agitates the gravel and sucks up the dirt. Most gravel cleaners you have to suck to get them working, as you would a normal syphon, but these particular ones made by Tetra have a self starting mechanism. The idea is, you rapidally plunge it up and down in the water and the syphon starts itself thanks to a non return type valve. I had tremendous trouble to get the syphon started, I had to agitate it so much that all the dirt which was in the gravel got whooshed up into the water, hence defeating the object of the excersise and leaving my fish tank cloudy for days afterwards. I also felt that the agitation really upset my fish. It was more expensive and less effective than the manual gravel cleaners. Utter rubbish.