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Water flow with HOB


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Hi all,

I am trying a hi tech planted tank with a few tetras, cories, and loaches for the first time. I need some advice to figure out what the circulation pattern is in a 45g tank with a Marineland Emperor 400 HOB. My tank setup is shown in the image below:



Right now I have the CO2 diffuser to the left of the HOB at the back. My C02 indicator on the other side of the tank and to the front. I am diffusing CO2 with the Aquario Neo Co2 Diffuser (Large) at the rate of 2 bubbles/second. However my NilocG Aquatics Co2 Drop Checker is not turning green.

I was wondering what would be the best course of action for me to get better Co2 circulation?

1. Move the Co2 diffuser to another location. Maybe the other end (right of HOB) of the aquarium at the back?

2. Get a nano circulation pump. Where would I place and aim this pump?

3. Switch from HOB to a canister filter and use it's movable intake/outlet to create circulation.

4. Increase the Co2 bubble rate slowly each day till the indicator turns green.

Any advice is appreciated!!



Edited by AquariumNewbie
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I would try to run the flow across the 36" length and have the CO2 diffuser under the HOB to hit the stream going across the tank. 

If you go with a canister, then build a reactor, which would give true 100% dissolution. "Cerges" reactors are easy to build.


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There's a few things you can do other than replacing your filter. Personally I don't think there's any reason to go with a canister of a HOB. 

First move your HOB. Ideally you would put it on the side of your aquarium so that the outflow pushes water the length of your aquarium. If you don't like the look of that then centered on the back is your next best bet. This way t he flow hits the front glass and deflects out to the front corners just leaving the back corners as dead spots. 

Next you should check for dead spots. Dropping finely crushed flake food into the HOB works for this. Anyplace food hasn't reached within a few minutes is a dead spot. 

If there are dead spots you have a few options. You can move decor or plants if they are blocking the flow, you can add an air stone or small sponge filter if the dead spot is in the back and easily hidden or you can add a circulation pump. 

Personally I feel every tank should have an air stone, and then you might as well run a small sponge filter if you already have an air stone running. 

Also if you do run a circulation pump you can put your diffuser directly under it to get better dispersion. 

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