What does low flow actually mean?

[seangee]

I always assumed it meant pretty sluggish and two of my tanks have been set up this way for some time. Today I added a Seachem Tidal 55 filter to my tank which has a theoretical flow rate of 1000 litres / hour. I guess this is more accurate than for a canister because the head height is not variable, but of course may be measured without media. I put this at the edge of the long side aiming across the short side (40cm) to ensure that much of the tank rmains calm.

I was a little surprised to see that my cardinals and pencilfish are happy to swim into the flow and spend a few minutes there at a time. They do spend more time out of the flow but I had assumed they would seek out quieter areas much quicker. Have I just been assuming slow meant slower than it needs to be?

 

[Jan Cavalieri]

I guess I always thought the flow rate was primarily to help distribute nutrients to the plants in the aquarium. Too slow and all the plants don't receive a distribution of plant "vitamins" from other parts of the tank. So if the flow rate is too low it can affect your plants health.

But I think you are referring to how the flow affects the fish in the tank. Are these two species river species that would be expected to like the fast flow of a river? If so, maybe they've gotten used to the stillness of the flow and this is just new to them. Heck - for all we know fish living in fast flow waters hate it would much prefer to be able to stop and rest. Maybe they are just "out of shape" and fighting the strong flow is something that they aren't ready to do. My Raspdora's love to play in the bubbler and will do so off and on all day, while the danio completely ignores it.

I think it's good with that powerful of a filter that there is still a lot of quiet areas in the tank. Perhaps I'm completely misunderstanding you.

 

[seangee]

Its about the fish. The SF profile for nannostomus marginatus (my pencilfish) states "sluggish, near still water" and for paracheirodon axelrodi (cardinal tetra) calls for "relatively slow moving water".

This has been the environment I have tried to create in the tank. I have never had a problem with plants but for me it is always fish first. If the plants can't cope with the needs of the fish they simply have to go.

 

[AbbeysDad]

Filter manufacturers rate the filter's gallons per hour (GPH) with no media. But who runs a filter with no media? I have a canister rated for 525gph, but with media, it's more like 100gph at best!

Hobbyists have become convinced that we need 4x to 10x GPH flow relative to tank size...and many believe "there's no such thing as too much filtration".
But good filtration is really about how well we filter water, not how much or how fast we push water through media. Besides, filters don't clean water, they merely make it look clearer. In fact, many filters become nitrate factories as the trapped waste decomposes and pollutes the water.

Disclaimer: Filters CAN improve water quality if/when they contain chemical media that adsorbs impurities. But these need to be reclaimed or replaced routinely to remain effective. It is most often more practical ($$) to rely on periodic routine partial water changes to better ensure ongoing water quality/purity.

Many hobbyists obsess over mulm (along with algae and snails)! They'll have over powered filters, add filters, or power heads for more circulation to increase filtration.
As I've written in other posts, not long ago on a FB fish forum, a member proudly displayed his 55g tank with three (3) large canister filters underneath! (ONE would have been more than enough). Water clarity is not necessarily a good measure of water quality! Many with large canister filters don't service them for months when it would be much better to routinely get the crud out of the system.

As to flow rates and fish, many think they may need to simulate a river because a given species in the wild is most often found in fast moving streams. However, although there are exceptions, many of the fish we see in the hobby are born and grown out in tanks or ponds and never lived in fast moving waters like their wild cousins. Besides, rivers and streams have eddies, depressions, rocks, and boulders where fish can rest. So having an oversize filter, or adding a filter or powerhead for more flow isn't really a good simulation anyway.
Yes we want decent circulation in a tank as it better distributes nutrients, eliminates thermal gradients, and creates a more uniform temperature. But it doesn't need to be a raging torrent.

For a time I ran a bubble bar on one side of my 60g, As much of a decoration as a gas equalizer. From time to time, I would see fish swimming up and down like crazy in the flow of the bubble stream. But what kid doesn't like a roller coaster ride.

 

[seangee]

As to flow rates and fish, many think they may need to simulate a river because a given species in the wild is most often found in fast moving streams.

My question is kind of the other way around. I am replacing the canister with a HOB. and was thinking to turn it right down. Just wondering if what I thought was low flow is actually much lower than it needs to be. No concerns about mulm and AqAdvisor (which I don't trust anyway) assures me that I urgently need more filtration as my filtration capacity is 25% of what I need. And a lot worse than that if I add in my MTS

 

[Byron]

My question is kind of the other way around. I am replacing the canister with a HOB. and was thinking to turn it right down. Just wondering if what I thought was low flow is actually much lower than it needs to be. No concerns about mulm and AqAdvisor (which I don't trust anyway) assures me that I urgently need more filtration as my filtration capacity is 25% of what I need. And a lot worse than that if I add in my MTS

I would not put an HOB on this tank. The canister is more in line though that is over kill too, or a sponge filter. The fish species mentioned do not need or appreciate currents, and in a tank that is 40 cm in length, even a canister is in my view way over the top.

My former 40g tank (90 cm length, 45 cm width) has a dual sponge filter connected to an air pump. Fish were 12 Parachierodon simulans, 15 Nannostomus eques, 2 Characidium fasciatum, 10 Hyphessobrycon amandae. The pencilfish and Embers spawned and fry survived.

With such forest fish we should keep in mind that the filter is really not even needed, or shouldn't be, except to keep the water clear (as opposed to "clean" which the plants and biological system will easily achieve). This is why I use a sponge filter, it does provide somewhat clearer water than without.

When I had a five-foot 115g running as an Amazonian riverscape, it has an Eheim Pro II canister. The spray bar was aimed into the left end wall, so the current went down the wall and across the tank. None of the plants moved in the current so it was very low. I had over 150 fish, characins and cories primarily, and it was interesting to observe that when given the options of more/less current, they remained in the non-current areas. The panda cories were the only fish that did spend time close to the filter bar end, which is to be expected given their habitat is the mountain streams in Peru.

The habitat should always be kept in mind, and replicated as much as possible, for every species. Tank raising does not remove inherent DNA traits.

 

[seangee]

I would not put an HOB on this tank. The canister is more in line though that is over kill too, or a sponge filter. The fish species mentioned do not need or appreciate currents, and in a tank that is 40 cm in length, even a canister is in my view way over the top.

I think I explained that badly. The tank length is 100cm long and the width is 40 cm. I have positioned the filter at one end of the back wall with the flow directed across the width. The width of the filter is only 15cm which means that 85% of the length is calm, and the half furthest from the filter is very calm indeed.

The aspect that surprised me was that when I had to flow at its maximum the two species mentioned would occasionally swim into the flow and stay there, but only for a few minutes at a time. Now that I have turned the flow down to its minimum rate all the fish occupy the entire tank My intention was to try to create a natural river environment with some flow and plenty of calm areas.

 

[Byron]

I think I explained that badly. The tank length is 100cm long and the width is 40 cm. I have positioned the filter at one end of the back wall with the flow directed across the width. The width of the filter is only 15cm which means that 85% of the length is calm, and the half furthest from the filter is very calm indeed.

The aspect that surprised me was that when I had to flow at its maximum the two species mentioned would occasionally swim into the flow and stay there, but only for a few minutes at a time. Now that I have turned the flow down to its minimum rate all the fish occupy the entire tank My intention was to try to create a natural river environment with some flow and plenty of calm areas.

Fish swimming into currents is not unusual. They have the expectation that food may be coming in the current. They might also be looking for "fresher" water. I frequently see fish swimming into the Python current, and this is exactly the same reason (both things). But these are one-off, not permanent. Remember that currents from a filter are 24/7 and the fish have no escape so whatever we force on them is it.

Clarifying the tank length helps, thanks. But now I am even more certain the canister is sufficient. If you can see plant leaves swaying in the current, it is usually too strong; having this next to the filter return but nowhere else is fine. Even my dual sponge filters create more actual current than one might imagine they would.

 

[Back in the fold]

Byron, are you saying that you use air driven sponge filters in your very nice tanks ? I've seen your pictures but cannot recall seeing your filters in them. I have been looking at pictures of wild Killifish habitat on the AKA website and it looks an awful lot like your pictures. You are certainly doing something right.

 

[Byron]

Byron, are you saying that you use air driven sponge filters in your very nice tanks ? I've seen your pictures but cannot recall seeing your filters in them. I have been looking at pictures of wild Killifish habitat on the AKA website and it looks an awful lot like your pictures. You are certainly doing something right.

Yes generally. I have a single sponge in my 10g, and dual sponges in the 20g and 29g. The 33g has an interior Aqueon Quiet Flow filter, and the same in the 40g. The latter had a dual sponge until I moved in May, and it now houses my 50 cories who stir up the sand all day long and the sponge cannot keep the water clear so I put in the Aqueon and it is now fine except when they are fed, but that is OK.

The photo below was the 40g before the move, and it had a dual sponge in the right rear corner; you can just make it out, behind the "tree trunk" wood.

 

[FishGuest5123]

I have changed to air driven sponge filters in 6 of my 8 tanks. I still have an Aqua Clear in 2 of them also. They all look clear and clean. The amazing thing is that I always had nitrate issues in my 55G due to goldfish. I had an aqua clear70 and a Aqua Tech 50 in it. I had an extra dual sponge filter for up to 50G so I added it to the tank also. Ironically, my nitrates are no longer an issue. I contribute a lot of this to the sponge filters.