I think this is one of the most common reason's people have issues with algae. Even with stated pump rating, all the fittings create pressure losses that cut that number in half. For a 100 gallon tank, I don't think there are any canister filters that can handle 10x turn over rates?

I think of flow and turnover as separate requirements.
Turnover is about the number of times the water passes through a filter and the optimum number depends on the amount of filtration needed. Usually at least 10x. This is where the more you have the better it usually is.
Flow is about current inside the tank and is not about the amount of filtration needed. It is about how well oxygen and co2 can be distributed throughout the tank, and harmful gases like hydrogen sulfide can be removed, and also about the welfare of the inhabitants.
Due to different ways in laying out the outflow, plants etc. the two are only loosely correlated. So OP would need to be more specific. I think this is a trickier question for low tech low maintenance tanks which rely more heavily on the substrate to produce the nutrients required my feeling is the layer of water above the substrate should not be circulated as much in order to allow for some anaerobic activity to develop.

I have a 65 gallon and added the smallest Aqueon Circulation Pump. It's suggested for 20-40 gallons and runs 2.6 watts, 500 GPH. That little thing moves some water! I'm still moving it around the tank to find the spot I like best that doesn't disrupt the plants too much. I also only run it for 6-8 hours per day.

I technically have 250x turnover in my sump display: https://www.plantedtank.net/forums/12...ml#post9186113

Its a DCS-4000 pump moving about 4g of display. The flow is perfectly uniform through a sponge-wall, and is surprisingly subtle.

I have a theoric 8X in my 65 gallon tank with a Eheim 2217 and one Hydor Koralia 250GPH. I could aim for better, i may aim for 15X in the future.

However some fishes like the gouramis, bettas, prefer quiet waters and maybe should not go into such a tank.

Michel.

I don't think big flow hurts, but not even in my top 10 for a successful planted tank. If you look at most Eheim Filters their flow is always much less then the competition for the same size setup, because they believe in efficiency of bio-filtration not turnover.

I think my 125 hits 6-8x turnover (due to pressure losses; source pumps put out 1200GPH), plus has two in-tank powerheads for circulation. Seems like a good amount of current in tank - fish are fine with it, plants are fine.

One thing you lose out on with high turnover is breeding (baby fish can't deal with current), but this may or may not be a bad thing. Also, bettas & guppies are out - too much for them (based on internet research and their origins).

I suspect the answer to 'how much is too much' will relate directly to tank size, layout, fish, plants, and location of returns.

When a sump is available, we try to use one.
It allows room for more cleaning machines below the display tank.


The water that passes through the filters will increase and not bother the fish if a 2nd pump is added in the sump.
The processing speed of the water is increased with a simple task of a pump pumping up about 12 inches high, back to the start of the flow.

Cranking up my display pump just made most fish zip away to hide, unless it was a goby or pleco. They like it.

We use sumps for freshwater planted tanks that are heavily stocked with fish.
The fish need the circulation.

The sumps are quite large for more added water volume.
Without the extra 2nd pump, a sump needed a small circulation pump to stop the top-film in the sump.
I figured I'd recirculate upward to the filter instead.

A quiet Sicce pro 1000 (1000gph) 60W max and an Eheim 1692 (900gph)80W max. are used for sump recirculation.
A DC pump is great for the display tank.
These beefy little guys don't use all that wattage to pump 12 inches.
I have heard most pumps use 1/2 the watts just to run though.

The pricey Vectra M1 adjustable DC pump runs hot at high speeds, so we use the DC pump at 1/4.
I can turn it down to feed them or a notch or two up to clean up all the stirred up stuff.


The pumps are such an investment that the one sump is still using a plastic tub.
Really Usefull boxes are tough and work well in a pinch.

Crank up the speed of that sump.
The display tank's DC pump can be adjusted for day/night speeds or simple feeding on a soft mode.

PICTURED:
The white EcoTech Vectra M1: 2,100 gph, 80W max (used at 1/4 speed) is the main pump to display.
The Grey Eheim 1692: 900gph, 60W max is pumping back to an assorted stack of foam sponges that I treat like Poret foam.
I smack them out against a wall like a thick car sponge.

Whether the sump box is below or above a display, crank it up!

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The vectras are so nice. I am only able to use it on the lowest setting, my Mame overflow can't handle any more than that. Can i ask why you have PVC on the intake? I really wish they would come out with a vectra-S, that way I could use the Vectra-M on a closed loop for more flow.

I have a Vortect mp10 in my tank. 100% power during the day, then "nutrient export mode" at night. Opposite side is an ES-2400.


That's probably 40x turnover rate on my 90-P. I still feel like I want more. That means it's probably time to clean the canister.

I should take it off. I can't remember why I placed it on and left it.

I have a Fluval 106 which runs 550 LPH (145 US GPH) in my 10g tank. It's rated for 25 gallons and the flow is a little too strong. However, I just found out recently the Fluval canister filter has a valve which controls the water flow. The whole time i thought it was an on/off water flow. It's just a gray/white lever which you can lift up or down to control the flow.

Here's a link below of the part:
106/206/306/406 Aqua-Stop with Integrated Valve | A20061 | Replacement Parts | Fluval

I have a 3x turnover in all of my tanks (theoretical turnover is 5-6x but with losses due to plumbing and filter material it gets cut in half), which is sufficient when using a spraybar over the full length of the tank.
any additional circulation is not needed, even the substrate remains clean.

so how much is to much?
basically everything more that a 3x turnover rate is unnecessary if you ask me, but it really becomes to much if the fish constantly have to swim against a strong current and/or struggle to stay in one place, except for reef tanks and some spices that live in fast flowing water.

I technically have at least 10x in my 75g

IMO powerhead placement and how the water flows throughout the tank is more important than raw GPH

I also run an EHEIM 2217 on a 20 long that works nicely for me. that is probably 10x turnover as well. do I really need that much? probably not

having said that I am going to introduce pearl gouramis into that tank in the next few weeks and they are not gonna like that much flow lol. gonna have to tone it down

so how much is to much?-- as long as the plants don't get uprooted and fish can still swim.