Air driven filter question

[Mikeyboy123]

I may have posted a similar question before but can’t seem to find it in my posting history.

Anyway, I am in the process of setting up a new tank – Aquael Leddy 40, 25 litres.

It came with a 300 lph ASAP filter but I really don’t want that sort of turnover in my tank. I know you need to take the flow rating with a pinch of salt, but I recently had a 150 lph mini filter in my 18 litre nano and that was way too powerful, so I think a 300 lph filter in the Leddy will also be too much.

I am looking at alternatives and have made some air driven filters with bits and bobs I had lying around. I am wondering about placement of the uplift tube. I have noticed that many air driven filters, particularly sponge filters and box filters etc, are designed so that the top of the uplift tube is well below the water surface. Years ago, when I ran UGF, I always made sure that the top of the uplift was at or just above the water line. I’m wondering why so many air driven filters have uplifts under the water line.

Part of me is thinking that there will be back pressure from the water trying to get into the top of the uplift which will reduce effectiveness of the filter. Another part of me is thinking that can’t be the case because so many of these types of filters are in use and people seem to think they work well.

Can someone explain why the back pressure doesn’t negate (at least partially) the upwards flow of the water? I realise it is a mixture of water and air, and I wouldn't expect the back pressure to stop the air coming out of the uplift, but I'm thinking that whilst the air escapes out of the uplift, the water may be left behind, and so instead of a constant flow of water up the uplift to be replaced by new water flowing through the sponge, you just end up with the same water gurgling around in the uplift.

Sorry if this a stupid question.

Grateful for any input.

 

[Back in the fold]

Air driven filters are the best. You can get extenders to put the uplift tube higher if that's what you want. You can reduce or increase the air. No impellers to clog or break. Even when the thing is totally clogged you still have water agitation at the surface from the air bubbles. You can put whatever filter media you want in them or have the very simplest of all air driven filters, the sponge. You can use an under gravel filter plate to eliminate all space taken up. Fish don't get caught in sponge filters and fry can feed off them too for a bit. Best of all is air drive filters are cheap and have no moving parts to wear out and break. They just don't have the WOW ! factor of power filters. No filter at all will ever take the place of regular water changes , smart feeding and general cleanliness so you can't go wrong with air.

 

[Lajos_Detari]

I will answer the first part of your questions as I don't have time to digest the second part of your questions.

I check the internet for your tank size and filter.
Your tank size is 41*25*25cm.
Your filter is internal filter Aquael ASAP 300.

I'm afraid that the filter with flow rate of 300 liter/hour will be too strong for your tank size.
In my opinion, a filter with a flow rate of 300liter/hr is more suitable for a tank with 60cm long.

By the way, is the filter flow rate adjustable?
If the flow rate can't be adjusted, then perhaps you can wrap around the front part of the filter with some foam/sponge pad to reduce the flow rate.
You can use a cable tie or rubber band to tie the foam pad around the filter.

Another method to reduce the impact of the fast flow rate is by putting the filter at one end of the tank instead of in the middle of the tank just like in the video below.
Make use of the length of the tank to reduce the impact of the fast flow rate..
I hope you can understand my explanations.

Aquarium Set LEDDY Day & Night 40

Aquarium. Free Hotline: 0800 55 66 40 541.

www.olibetta.com

Aquael

Najwyższej jakości sprzęt akwarystyczny od polskiego producenta - bogata oferta z szybką dostawą!

www.aquael-aquarium.co.uk

 

[GaryE]

I use air on a central piping system. I suspect that below the surface air is a question of noise. My filters that 'spit' water have excellent oxygenation abilities, but in the living room they would be annoying. Where I have them, they're great.
They also lead to a touch more evaporation. So I suspect it's convenience behind the filter set ups, more than function.

 

[Mikeyboy123]

Thanks for your replies. I've made 4 air driven filters of differing design, all with 90 degree bends at the top of the uplift. I've tested them all out and all of them work just fine with the top of the uplift above the waterline so I'm happy with all of them. I still don't really understand how having the top of the uplift below the water line works for the many sponge and box filters that I have seen that are designed like that, but I guess it must work. But it's not a concern for me so it's a moot point for me really.

 

[itiwhetu]

Having the air lift above the water line will give you better water flow as there is less resistance through air than water. If the air lifter is below the water line, the water in the tank acts as resistance for the water that is moving through the filter, therefore less flow.

 

[Mikeyboy123]

Having the air lift above the water line will give you better water flow as there is less resistance through air than water. If the air lifter is below the water line, the water in the tank acts as resistance for the water that is moving through the filter, therefore less flow.

This is what I suspect and is the crux of my question. As I say, not an issue for me, but I was just curious as to why so many air driven filters seem to have this fundamental design flaw. I’m not saying they don’t work at all, but it seems pretty obvious that a filter with an uplift below the whaterline will work less efficiently than a comparable filter with an uplift that is just above the waterline.