Fluval Flex Filtration Flaws?

[Brit’s Fish]

This is going to be a long post but I am at my wits’ end and about to just throw this tank out. Ugh.
I have owned my 32.5G Fluval Flex for about one year now. I do 20% bi-weekly water changes but within a few days of doing the WC, the water starts to get this brown film on the top. It gets thicker as the days go on. I literally will take some paper towels and lay them on top of the water to get it out. I don’t know what it is & how to get rid of it. My overall conclusion is that the filtration in the tank just kind of sucks & I’m looking for opinions.

It’s stocked extremely lightly - only a single, murderous Pixy Hawkfish, affectionately named Rocko, one emerald crab, one Halloween hermit crab, a fighting conch, a large brittle star (also about 1 year old) & various other snails and hermits. There are also TONS of little white brittle stars all over that kind of showed up out of nowhere. I like them.
started the tank with new live sand & Caribsea Life Rock.

I still have the stock hood on this tank & the stock pump as well. I’ve added two Hygger mini wavemakers at opposite ends of the tank, slightly offset but on synchronized schedules. Literally the only reason they’re there is to try to break up the film on the surface. I have the InTank media baskets as well. The thing that bugs me about this tank is the way the “overflows” work, if you can call them that. There is a top overflow and bottom overflow on both sides of the tank and unlike every other tank I have (this is one out of 5 SW tanks) the overflows are horizontal instead of vertical. The surface doesn’t seem to be getting skimmed.
the Fluval skimmer that’s made for this tank is utter garbage and the water level needed to use it is almost unobtainable 100% of the time. I have a reef glass skimmer I’m willing to try out on this tank, but I’m also sooooo fed up. The film on the top of the water actually helps me to see just how weak the pull into the overflows is & how there’s virtually no surface skimming happening at all.
Should I try the skimmer? Should I try upgrading the pump? Should I just switch to another tank all together?

There is an abundance of coralline algae and also a ton of aiptasia because Aiptasia X hasn’t worked too well for me in this tank & Rocko eats any living methods of controlling them. Could Aiptasia somehow be affecting the water quality? It feels far-fetched but I’m willing to consider anything at this point.

I used to have more corals in this tank - mostly euphyllia, zoas, Xenia, GSP & mushrooms. Once the hammers and frogspawn started bailing, I removed them one by one & put them in my other tanks where they’ve all pretty much recovered. I also removed most of the zoas and mushrooms that were not attached to the main rock structure. Not sure if the issues with the euphyllia were from the water or lighting or what? The GSP, shrooms and Xenia that are left are doing great, not surprisingly.

Parameters as of this morning (test kits listed after params):
Temp 76.5 Hanna
Salinity. 1.025. Hanna
pH. 8.0. Red Sea
PO4. 0.10. Salifert
Nitrates. 20 Hanna
Alkalinity. 6.7. Salifert. (I know this is low - dosing brightwell alkalin8.3 for it)
Magnesium. 1380. Salifert
Calcium. 480 Salifert

 

[Brit’s Fish]

A couple pictures if this helps. Also, the photos of the back filtration, if that helps. The one with the arrows is a decent demonstration but I have gotten rid of the sponges and upgraded to the InTank media baskets which force the water to only flow over the top of the basket and down into the return area instead of letting half the water bypass it like in that photo.

 

[mdb_talon]

I had a friend who had many of the same complaints. He bought something like below and it made a world of difference. I am not sure if this is exactly what he got, but I know his solution included covering most of the intake (completely blocking the bottom ones).

Top Upgrade Kit for Fluval Flex 32.5G, Intake Covers Spray Bar and 12 XXL Lid Props, Set of Four Intake Covers, XXL - Etsy

This Aquariums & Tank Decor item by LidPropzShop has 83 favorites from Etsy shoppers. Ships from Goshen, IN. Listed on Mar 8, 2024

www.etsy.com

 

[LiveFreeAndReef]

Maybe twist the outlets a bit so they're breaking the surface to get the surface scum into the tank/filtration? I get a little oil slick on my Flex 15, but I just kinda deal with it lol..

 

[Brit’s Fish]

Maybe twist the outlets a bit so they're breaking the surface to get the surface scum into the tank/filtration? I get a little oil slick on my Flex 15, but I just kinda deal with it lol..

I have tried pointing them in every direction i can think of and nothing seems to make enough of a difference. The corners are actually sticking out of the top of the water… but maybe that’s not helping? Could there be a loss of water pressure or something by letting air in?

 

[Brit’s Fish]

I had a friend who had many of the same complaints. He bought something like below and it made a world of difference. I am not sure if this is exactly what he got, but I know his solution included covering most of the intake (completely blocking the bottom ones).

Top Upgrade Kit for Fluval Flex 32.5G, Intake Covers Spray Bar and 12 XXL Lid Props, Set of Four Intake Covers, XXL - Etsy

This Aquariums & Tank Decor item by LidPropzShop has 83 favorites from Etsy shoppers. Ships from Goshen, IN. Listed on Mar 8, 2024

www.etsy.com

Thank you!! That’s a really good idea. I’ll check this out!

 

[Brit’s Fish]

Maybe twist the outlets a bit so they're breaking the surface to get the surface scum into the tank/filtration? I get a little oil slick on my Flex 15, but I just kinda deal with it lol..

Or are you suggesting that I twist them a little more vertically?

 

[LiveFreeAndReef]

I have tried pointing them in every direction i can think of and nothing seems to make enough of a difference. The corners are actually sticking out of the top of the water… but maybe that’s not helping? Could there be a loss of water pressure or something by letting air in?

I was thinking of maybe turning them so they're vertical, basically have one half out of the water? I dk, but that was my thought with my Flex to take care of the surface scum stuff.

 

[LiveFreeAndReef]

Or are you suggesting that I twist them a little more vertically?

Hahaha impeccable timing

 

[Reefer4fun]

I`d upgrade the pump. The overflow should help to capture the film and the filter media should remove it.

 

[LiveFreeAndReef]

I`d upgrade the pump. The overflow should help to capture the film and the filter media should remove it.

The issue is that the water level is the same in the back of the tank as the front, so it never falls into anything to get sucked into the filtration. It's not an "overflow", really just a guard to keep fish out of the filtration

 

[mdb_talon]

The issue is that the water level is the same in the back of the tank as the front, so it never falls into anything to get sucked into the filtration. It's not an "overflow", really just a guard to keep fish out of the filtration

Yup. agitating the water more as you suggest is good way to get it mixed up and get some through the filtration. Blocking off the bottom intakes and part of the top ones can make it function like a true overflow.

 

[Brit’s Fish]

Thanks all! I’m going to look into the kit to block the bottom overflows and twist the returns so that they’re a little more vertical. I really hope this helps. I can’t help but think that the overall design of this tank just kind of stinks but I do see several people who have pretty successful Flexes.

 

[DaddyFish]

I have never owned a Flex, but I've gawked at several of them. If they made a bigger one I'd have it!

Just curious if you have tested the return gph by having it dump into a partially immersed container or one gallon bag?

*** Edited to correct the flow numbers...
A 35 gallon tank needs about 250-350 gph flow. Measuring the flow with everything in place might tell you a lot about the possible need for a different pump.

 

[ahiggins]

Personally, I hate the “freshwater made” saltwater tanks because of that bottom “overflow”. I used a tank like that for a pico once, I siliconed it off first thing. I know you can’t really do that now but superglue might work?

 

[Brit’s Fish]

I have never owned a Flex, but I've gawked at several of them. If they made a bigger one I'd have it!

Just curious if you have tested the return gph by having it dump into a partially immersed container or one gallon bag?

A 35 gallon tank needs about 25-35 gph flow. Measuring the flow with everything in place might tell you a lot about the possible need for a different pump.

The look of the tank is what sold it for me! My husband loves having it behind his desk & if not for the filtration issues, I would like it as well. If I remember correctly, the stock pump has somewhere around 245 gph output, so I could definitely increase that. I will try the method you’re suggesting though just to see what it actually does.

 

[Brit’s Fish]

Personally, I hate the “freshwater made” saltwater tanks because of that bottom “overflow”. I used a tank like that for a pico once, I siliconed it off first thing. I know you can’t really do that now but superglue might work?

Yeah, I think this would be fine for freshwater but they missed the mark for saltwater. Superglue might work if I can’t get the custom made overflow blockers that someone mentioned earlier. Thanks for that idea!

 

[ahiggins]

Yeah, I think this would be fine for freshwater but they missed the mark for saltwater. Superglue might work if I can’t get the custom made overflow blockers that someone mentioned earlier. Thanks for that idea!

No problem
It’s nice for the cost of the tank, they charge sooo much for the all in one saltwater tanks (I have a 10 and 30 lol) so I get the savings. Just takes a bit of customizing

 

[MaxTremors]

A couple pictures if this helps. Also, the photos of the back filtration, if that helps. The one with the arrows is a decent demonstration but I have gotten rid of the sponges and upgraded to the InTank media baskets which force the water to only flow over the top of the basket and down into the return area instead of letting half the water bypass it like in that photo.

I would try blocking off the bottom intakes on the overflows, forcing all of the water to go through the top. You could superglue or silicone a piece of black acrylic over the vents). It may not seal them off completely (which probably good so that there is some flow through the bottom of those chambers. I would also aim the wavemakers you have at the surface so get a lot of surface agitation (make is so the water isn’t still enough to even notice the film. All that said, this issue isn’t hurting anything, all tanks without decent surface skimming/agitation have this problem. I would also consider upgrading the return pump, the more water circulating through, the more likely you will create enough of a flow on the surface into the overflow that it will catch all of it. Let us know what you end up doing, AFAIK this is a pretty common problem with this tank (on of the reasons why when I was looking for a new AiO last year I didn’t choose this tank).

 

[LiveFreeAndReef]

Thanks all! I’m going to look into the kit to block the bottom overflows and twist the returns so that they’re a little more vertical. I really hope this helps. I can’t help but think that the overall design of this tank just kind of stinks but I do see several people who have pretty successful Flexes.

Just wanted to follow up, I turned one of the outputs (almost) verticle so that it's breaking the surface and Im already seeing the oil slick break up!