15 foot tank and sump w/ bottom drain up to weir

[NetMax]

Building 15 foot long plywood/formica tank, 28" high by 16.5" wide, planted, display tank (Discus etc). Using Herbie/Durso siphons on both ends, to sump underneath, returning up the center to opposite side (picture below, open to any comments or questions). My concern is in regards to the weir intakes. Normally plastic weirs have an upper grill and sometimes a lower grill with an internal baffle up to the upper grill. I prefer to pull about 10% from the surface (protein layer management) and 90% from the bottom (least oxygenated water). In the past, I've used UGF plates along the front, covered by river stones in less planted cichlid tanks, connected to a canister (or HOB) intake pipe (makes a 24/7 gravel vacuum). I'd like to do the same, pulling from under a false bottom along the front, but this time under some 4-5mm sized substrate, lightly planted, and using the water pressure to rise up behind the first weir (baffle) and to conventionally flow down to the sump. My concern is this setup is not easily changed if it doesn't work as designed, and I haven't seen this configuration used before.



Thanks for any comments or recommendations.

 

[Backfromthedead]

Ambitious project, i like the simple, unobtrusive plumbing layout. I would consider installing some of the elements like the false bottom in such a way that it could be removed somewhat easily if you wanted to change it up.

The baffled overflow should work very well to get something like that 90/10 mix you want...just adjust the flow so the water level barely breaches the top weir(grill) and that would mean most of the flow is coming from the bottom. But like you said, ive never seen such an overflow in operation.

You mentioned oxygen levels as your reasoning for the baffled overflow. Just curious, do you have any information thats led you to believe there is significant DO stratification in a tank this size? Ive sorta been under the impression that if you have reasonable flow/turnover that a tank this size would be pretty well mixed/saturated throughout. Even if it was an issue i would probably just use a couple airstones to provide an upwelling current.

 

[NetMax]

Thanks, I had an overgrown 90g and every Otocinclus I added died within 2 months. I know the issues with Otos and tried different sellers, strains and foods. The mortality period suggested it was not acclimation or a pathogen. After ruling out water parameters (F, pH, gH, kH, CU, PO4, NO3 & TDS), and reading about possible sensitivity to low O2, I pulled out two pails of plants, and the one remaining Oto (#14) is now doing great. Also in pond filtration, bottom drains are generally viewed as superior - removing detritus with water which may be cooler and more stagnant (lower O2). I don't think a typical aquarium with good filtration would benefit significantly from a bottom drain (filter intakes are already fairly low), but I tend to put a lot of 'stuff' in my tanks that impedes circulation, and I don't like to compensate by adding additional flow. I'll be using 1,500 GPH x two for this tank, which is not a lot. Because of noise, I stopped using air pumps (40 years ago) and just gotten used to never using them. If I need to play with flow (eg: for caves or deep pockets in structures), I'll pull one of my return nozzles down.

I think the above design will be a 'balancing act' to set up, so four adjustable baffles at skimmers and inner baffles, and finding the right substrate size & depth to use. The two problems are that I have no sense of the flow restriction the gravel will create to a 'gravity' flow (may need significantly lower inner baffle heights which cause sump overflow concerns on power failure), and I suspect that the flow resistance could be highly variable to detritus that gets caught up in it (so very well rounded stones of just the right size are needed). I'm tempted to use powerheads to pull from underneath into baffle chamber, and the upper skimmer grill will be the safety (normally pulling 10% but flowing backwards to prevent overflow). While this seems logical (less reliance on gravity and changing conditions) it would make my design even more unconventional.