I’m sorry but I’m confused by what you mean, do you mean internal filters? I thought the idea of HOB filters is so that they are not submerged inside the tank?
I will have to have a look into that to see if I can find a way of reducing the noise discreetly. That’s also why I thought I’d ask here, in case there was some amazingly quiet HOB that I’m not aware about that doesn’t need manual alterations.
I heard seachem tidals are great, but they look huge! Probably too big for a shallow tank? 🤔
HOBs come in two sorts, basically, either the pump sits in the HOB bit and sucks water out of the tank into the filter case, or the pump sits inside the tank, part of the inlet assembly, and pushes water into the tank. The Seachem Tidals you mention do that, which was what attracted me to them, but you're right, they're huge. I went for the 110 and it was a vast thing. Even dry, it was hard to separate parts as you would need to for maintenance, and because there are three separate inlet points, it's pretty much impossible to make it safe for shrimp or fry without wrapping it in swathes of foam. I'm sure that in big tanks for big fish they're brilliant, but wouldn't suit your purpose. The principle of pump in tank, however, makes great sense: it's quieter, and the filter is much more likely to restart automatically after a power cut, without needing manual priming.
As an alternative, slightly left-field approach, Marina do a
hang-on breeding box which functions more or less like an HOB, it just is designed to hold fish rather than filter media, but I believe some people do run them as filters. Water uplift is an air-lift, apparently a bit noisy but can be
modded, and I dare say a bit of ingenuity with a pump might be possible too. The marina box is not too deep, but several litres of volume would hold a lot of media.
I'd love to find a small HOB with the pump in the tank and an easily fry-proofed inlet. If you find one, please post about it.
