Fluidized bed in a wet dry filter ?

[B_IN_SD]

I have a used wet dry filter that I traded for store credit at my lfs and I would like to add a fluidized bed filter to it. Are there any pro's or con's to this ? The wet dry is rated for a 150 gl tank and I would be using the skimmer for the fdb. The shimmer just sits in 2 rails of the wet dry and can be easily removed for cleaning.The dim's of the skimmertube are 3 3/4'' dia and 13'' tall.
I would like to glue the skimmer to the bottom of the wet dry and use a power head to to set the sand in motion. The pump will need clean water so the little holes of the fdb will not clog up so I will have to drill a hole in 1 bulkhead of the w/d under the bio ball section. Then the water that has gone through the fdb will go back over the filter pad and bio balls.
The first picis the stock wet dry filter the second pic is with the skimmer sitting where it would be glued.

 

[timeneverfreezes]

The pros to a FBF are that it creates an enormous amount of surface area for BB. Some cons are, if for some reason power is lost and returns it might not work by itself. Depending on the amount of sand media in the filter the pump might not be able to re-fluidize the sand. If this happens while you are away, say for vacation or even work, Etc. the BB starts to die very rapidly. In effect it becomes smothered in the sand, starving it of oxygen rich water.

I would suggest not gluing the skimmer tube to the bottom of the sump. Its "easily removed for cleaning" and probably should stay like that. Just attach a bottom to the tube instead. Also instead of drilling any holes try looking into a pre-filter for the powerhead, Marineland makes some decent ones.

I plan on making a FBF when I get a chance so I know that there are a ton of articles by reefers all over the net. Check them out before you start, you'll be glad you did.

 

[mrunlucky07]

That is a nice acrylic tube and perfect for a FBF. I would make it into a stand alone unit with a powerhead hidden in the tank though.

I have several FBF and love them. From my personal experience I do not recommend running them from the sump. Two main reasons. First they are very sensitive to flow rate. A tiny change in flow rate and the sand level can change a lot. I add water to my sump about once a week and the sand level in the FBF was constantly changing as the waterline in my sump changed due to the head pressure on the powerhead. The second problem is the restart everyone mentiones. If run from the sump and the sump waterline is below the top of the FBF the water wants to drain out and make a hard restart.

I have had great success with mounting the FBF below the tank waterline, similiar to a canister filter. There is constant head pressure on the pump so the sand level does not fluctuate, and when the power goes off there is no back presure so the bed collapses very slowly and always restarts.

 

[FireMedic]

Mr Lucky is on to something. I completely agree. Just be mindful of the flow rate. (dwell time = increased efficiency)

 

[rallysman]

I made a FBF in my sump a while ago but took it apart because how I had designed it was too loud.

 

[B_IN_SD]

Thanks for the advice every one. I spent the day looking for some weld-on #3 today with no luck. Oh well back to ebay. Tomorrow at work I am going to make a bottom and diffuser then it's sit and wait for the cement.
I did a quick mock up in a 10 gl tank and it looks like a aqua clear 802 has the flow to make it work but nothing is final yet. I will post another pic when I have the fbf running.

 

[justin guest]

Hi

My two cents worth;

When running a fbf in a sump you just have to make sure the fbf is in an overflow chamber with a constant water level. The top of the filter should also be around the water level of the chamber to avoid compaction problems when the bed collapses. From your pictures your filter fulfils both these criteria as skimmers also often have similar constraints. To stabilize media height just use a slightly larger grain size and up the pump size slightly to suit. The best pumps for fbf have a higher maximal water head than normal powerheads which makes restarting easier. The eheim range of pumps is a good (but expensive) example. Pump the water through a couple of inches of coarse rounded gravel in the bottom of the fbf (gravel shouldn´t move) as well to ease startup problems. Don´t forget to occasionally clean the gravel though.

j<><

 

[timeneverfreezes]

^
i
i
i Very good advice, B_IN_SD im glad you started this thread!

 

[B_IN_SD]

I made a few parts today. rallysman gave me the idea for a top I drilled and taped 2 holes 3/8 npt. for return water I will plumb these to return under the waterline so there will be no noise.

 

[B_IN_SD]

This is what it looks like in the skimmer tube. The center hole will be for the water inlet. I am looking for some clear acrylic tube for this.