[Todd L]

Hello all,
A few weeks ago I posted a question about my phosphate levels, and someone recommended I install a phosphate filter which I did. I picked up an Aqualine Phosphate Filter and it seems to have worked well. The level is still not at 0, but pretty close.

Here are my questions/concerns. It seems after thinking about what happened here I came up with some thoughts and wanted to bounce them off of some more experienced minds.

A few months ago I built a HOB fuge that I intended to use more as an algae filter. I modeled it after some of the HOB units i saw online. I set it on a narrow base I also built that fits behind my tank so it sits slightly higher than my main tank and simply drains through a bulkhead. In it I placed LR, about a 3" sand bed, chaeto, and a few other types I can't remember. I modified my skimmer so that the output fed the fuge.

At first everything seemed to be working really well. The Maidens hair algae I purchased seemed to flourish at first, but over time I noticed all of the algae I had in there seemed like it was disappearing.
At about the same time I noticed this, I had an incredible amount of algael growth on my glass, which I found was fed by the excess amounts of phosphates and my recent upgrade to T5 lighting. The minds here are what directed me to get the phosphates taken care of which I thank you for, but I needed to know why the phosphates got so highin the first place. I had to assume they were always there as I had been overfeeding, but why the sudden increase!

When I would rotate my chaeto, I noticed some of it seemed like it was decomposing along with some of my other algae in there. I finally took it all out of the fuge, and placed what was left in my main tank which at this point is all pretty much gone. So now as I write this, my fuge sits empty except for the bed.

Last night I decided to try to measure my flow rate out out of the skimmer, which fed the fuge, and it seems like it is at best about 20gph. Not nearly enough from what I gather from reading posts here! I'm assuming my phosphates increased due to decomposition of my algae due in turn to poor flow.

Ok....sorry for the long post here, but my questions are...

I have a lot of (I think?) caulerpa in my main tank already.
Should I remove it and place it all in my fuge? I'd like to be able to go back to just the LR look in my main tank anyway.
I know if I want to have the fuge be effective I need to increase the flow a LOT...to maybe about 80 or so gph at least? That's do-able with some re-configuration.
Should I just forget the fuge idea altogether? Is having algae in my main tank good enough? Is what I have any good?

Also.....it seems a 20gph for my skimmer seems barely good either...what should a good flow be for a skimmer

Tank parameters- NO2- 0, Ammonia- 0, PH- 8.2, Alk- normal range, NO3- <3, PO4- .1. Not perfect, but remember I do not keep corals.

Thanks for your input and huge apologies for the long post!!! Attached is a pic of the algae I have in my main tank.

[ejwsr]

First, did your HOB fuge/algae filter have an independent light source? You need a light for an energy source for photosynthesis to occur.

Flow rate. I would think that it is too high. A 46 gal tank should have a skimmer that processes 10% capacity per hour or 5 gph. The longer that the water is in contact with the air bubbles in a skimmer, the better adhesion to the bubble and the dryer the foam output.

Flow rate part two - Here is where there can be a great deal of debate, but it boils down to attaining two mutually exclusive goals:
High current in the tank
Low flow rate thru the filtration system.

High flow rates are good in the tank because it will keep detritus suspended until it hits your filtration system, keep corals and fish happy and healthy and there is an aesthetic value to seeing everything swaying in the currents.

Low flow thru the filter is critical for a few reasons:
In a natural system the nutrients can't accumulate because of the massive water movement. What nutrients are there are absorbed slowly by the algae and bacterial colonies. And slowly is the key for the closed tank environment.
Cellular respiration/metabolism is a slow process. The nutrients have to not only make contact with the cell, but in most case need to be passively transport across the cell membrane. Think about how an RO unit works and the picture becomes clearer. It takes time, osmotic pressure, etc just to get to the metabolic mechanism of the cell. The conversion from nitrate to N2, O2 , carbohydrate or protein synthesis also takes some time. It has been a long time since I studied molecular biology, but I do remember at least 6 steps or elements that have to happen.

You have to give it time to do it's thing, hence the low flow through the filter. Or at least through the algae refugium part of your filtration system.

[Todd L]

Eric,
Thanks for the reply...

I do have a light on the fuge, and have it on reverse cycle from the main tank.
I've always had a decent amount of skimmate off of the skimmer at the flow rate it has, which is not even close to what the flow rate is capable of! I'm not too worried about the flow rate in the skimmer and have never heard it should be as low as 5gph...are you sure???

I have a pretty good level of water movement inside the main with the filter and an internal pump, and agree with you there.

My question was really directed more towards the flow rate in the fuge and whether or not it was the slow flow that compounded the deterioration of the algae I had in there. When I first set it up it seemed like the algae flourished, and I noticed a good amount of growth. It was about a month after that I saw the condition of the algae degrade. The chaeto I had basically disappeared, and what was left in there was mucky, the caulerpa went from a vibrant green to a pale whitish hue and disintegrated and the maidens hair I had disappeared also.

I had always read a *low flow* rate for a fuge would be considered to be about 80gph. I hadn't tried to measure the flow off the skimmer and just assumed it was about 80 or so as it is rated for a much higher flow, assuming it would be enough to properly feed the fuge.

So while the 17-20gph (and that is really on the high side) the skimmer is set at may be enough for skimming purposes, I have to assume it is not enough of a flow rate for a fuge and allowed for *dead spots* inside my HOB fuge.

Thoughts?

[ejwsr]

Todd,
I knew I was missing something important. By routing your skimmer outflow through your refugium you are oxygenating the water. The algae needs CO2 for carbohydrate synthesis. Since high O2/low CO2 levels exist in your fuge, you are starving the algae since they cant make their own food any more. What I would is route water from your filter system (put a T in the return line with a small valve so that you can adjust your flow) through your fuge. There should be plenty of available CO2 for your algae.

Back to flow rates for a moment. I have a Current Nano Fission skimmer in my NanoCube. It has an 84gph pump. Due to how the air is introduced (through the pump suction) the water flow is cut way back. I would wager that my water flow through my skimmer is at or below 10 gph.

[Todd L]

Eric,
That all makes sense! Thanks!
I'll make the changes!

[ejwsr]

Glad to be of help!

[reef4gsp]

I just wanted to comment on your post ejwsr. Being new to the water quality of sessile inverts, I take that information with a whole DASH of salt. It completely skipped my mind, the oxydizing affect on the CO2 content of the water. This will play into much consideration for my new sump design. Plus: I'm from sacramento also. lol

[ejwsr]

The guy to talk to, besides me, would be Tim at Exotic Aquarium on Franklin and 44th in Sac City. Great guy. In fact the all the salt guys there have been "on it" 99.9% of the time.