Maximising Biological Filtration - 6 foot tank

[Ghoti]

I am looking to boost the (biological) filtration capacity of my 1800x470x640 planted tank (capacity 537 litres)

I am running a 1200lph Otto PF300G canister (rated for 400lt) and an overhead wet/dry trickle filter fed by 2x900lph powerheads. The canister is packed with sponge, noodles and 100ml of purigen with each layer separated by filter wool pads.

While parameters are generally ok (ph 6.5, Ammonia 0, nitrITE 0, TDS 100-115), I do struggle keeping nitrATES below 10ppm even with twice weekly 30% water changes. Admittedly the stock level is very high at the moment following me moving all fish from my four foot tank into this one so the Discus can have their own tank for a short while.

Along with reducing stocking levels I want to boost filtration, preferably without increasing flow. I have 6 discus in QT destined to return to this tank once I am happy with it.

I considered going with a sump but counted this out due to the mods required to both tank and cabinet. Also considered FBF (both DIY and Otto) but discounted due to fears of the sand packing down during the frequent power outages we experience during August/September. That leaves me with the following options:

1) Use the Otto PF300G as a pre-filter and add a 30lt DIY biological filter/external heater. The unit would be constructed from a food grade screw top watertight container (sealed with an o-ring), filled with noodles or matrix, and with a heyco cordgrip providing a watertight seal around the heater. An external heater has long been on the DIY wish list.

2) Add an Otto PF450G (1800lph rated for 600l) canister filter in series with the PF300G using the 300 as a mechanical pre-filter and the 450 as a biological filter and return pump (i.e. remove impeller from 300 & don’t plug it in).

3) Simply add an Otto PG450G as an extra filter, plain & simple.

So, why don’t I buy a Fluval FX5/Eheim pro? I'd like to give some excuse around redundancy, but trugh is primarily $$$$, and I’d also wonder if they’d fit in the cabinet. I’ve had my Otto longer than I can remember (perhaps 18 years), never skipped a beat, haven’t even changed an o-ring. So I’m reluctant to change brands.

FYI target stock is:
8 x Discus
5 x Redline Torpedo Barbs
10 x Cardinal Tetra
5 x Neon Rainbowfish
5 x Otocinclus
5 x Peppermint BN
5 x Dwarf Chain Loach

I’d certainly appreciate some expert guidance on the best option(s) to minimise nitrates & maximise stock carrying capacity.

Cheers,
Scott

[ILLUSN]

If your tank is planted plants should keep the no3 down failing that get rid of the trickle filter and add another canister. trickle filters mix air with water and work excellent aerobically, to remove no3 you want to filter anerobicly. If you daisy gain the 2 canisters together (and power only the second one) the water leaving the 1st will be oxygen poor allowing the second to break down the no3.

Just make sure the outlet is above the water surface so as it re oxygenates as it reenters the tank

[Ghoti]

Thanks Illusn, particularly for the tip on re-oxygenation as I would have used existing (submersed) spray bar position.

Not sure I understand the tehory behind decommissioning the trickle filter when I add the extra canister.

Is it because the trickle filter becomes another source of nitrates?

Cheers,
Scott

[ILLUSN]

trickle filters work very well aerobicly they mix air and water together as a result they smash ammonia into no2 and into NO3 but have 0 capacity to breakdown NO3 you could leave and just fill your second caister with matrix or de nitrite and hope that its enough to keep your NO3 down, also try floating plants likewater sprite