Coral tank water flow patterns

[dorvain]

Been rearranging powerheads in my 75 gallon mixed reef trying to fix dead spots behind the rock arch where detritus piles up and my Duncan stays closed half the day. Return pump on back wall, two small powerheads left and right mid tank, LED medium par, alk 8.3, calcium 430, mag 1320, torch upper right, zoas mid shelf, two Clownfish and cleaner shrimp. Should flow cross the tank in one direction or bounce randomized? Not sure what pattern actually works for mixed corals.

[lynxfang]

Mixed reefs do better with alternating cross flow than one constant direction in a 75 gallon. Aim return pump along back glass low for baseline turnover, run left powerhead wide pulse sweeping front to back, right powerhead opposite phase so flow collides mid tank and breaks up arch eddies. Target twenty to thirty times turnover split across three outlets. Duncan inside arch wants gentle indirect ripple not direct jet, point heads to skim the arch opening not the polyp face. Torch upper right needs moderate random pulse for gas exchange without folding tissue nightly. Zoas mid shelf tolerate more chop. Turkey baster arch sand weekly still, flow pattern reduces buildup frequency. Canister filter intake on end panel pulls slow water, offset powerheads toward opposite corner.

[Tealux]

Dead zones behind rock arches are almost always low exchange pockets where detritus settles faster than bacteria can process. Cross flow pattern beats single direction gyre in mixed layouts because torch, Duncan, and zoas want different shear levels on the same rock structure. Return pump low on back wall, left and right powerheads on offset pulse timers, thirty to sixty second variance breaks predictable eddies. Duncan closed half the day inside arch often means tissue is getting periodic blast plus shade, relocate slightly forward or soften pulse aimed at opening. Alk 8.3 calcium 430 mag 1320 stable, medium par LED unchanged. Canister filter intake creates quiet corner on same side, compensate with powerhead sweep across that end.

[starwave8]

yeah cross flow randomized pulse is the move bro not one direction hurricane. return pump back wall low baseline, left head wide sweep front to back, right head opposite phase so water collides mid tank and flushes that arch eddy. duncan inside arch wants indirect ripple at the opening not jet on polyps. torch upper right needs moderate random pulse, zoas mid shelf handle more chop. turnover twenty to thirty x split three ways. turkey baster arch sand weekly still but pattern cuts buildup. canister filter intake pulls quiet water same end so offset heads toward opposite corner.

[coastguard1]

For a 75 gallon with arch rockwork, alternating cross flow prevents the detritus sump you describe behind center structure. Constant left powerhead while right pulses every eight seconds can leave predictable dead pocket, match both on offset pulse with wide dispersion. Return pump along back glass feeds baseline exchange, canister filter intake on end panel creates low flow corner you must sweep. Duncan lower in arch needs tissue flutter without folding, aim jets across opening not into polyp crown. Torch six inches up right wants moderate random flow for sweeper clearance. Alk 8.3 calcium 430 mag 1320, medium par LED, Clownfish and cleaner shrimp fine. Baster arch sand weekly until pattern proves out.

[dorvain]

Left powerhead runs constant, right one pulses every eight seconds. Arch dead zone sits about six inches behind center rock where sand gets brown film weekly. Duncan on lower shelf inside the arch, torch six inches away upper right with sweeper room now. Would running both powerheads on pulse mode fix eddies or make it worse for soft corals? Tank has canister filter too if that changes intake patterns.