Rowdy and 6-Line,
I don't want to beat this topic to death, but last night I did a little reading and research on phosphates since they are a primary factor in causing algae problems. Here are more of my thoughts....
I have a copy of "The Reef Aquarium, Vol. 1" by Sprung and Delbeek, and on pgs 262-265 there's some good info on phosphate (PO4) chemistry and reduction. In a nutshell, and liberally translating/quoting from the book, PO4 exists in both organic and inorganic forms. If readily available in organic forms, it can lead to massive algae blooms. The inorganic forms have limited occurrence in the water since it is quickly consumed by plants, and readily blows off into the atmosphere as aerosol from the bubbling action skimmers. PO4 is also an essential component of living tissue, so it isn't possible to eliminate it entirely from a tank unless the tank is literally devoid of life (wouldn't be much to look at, would it?).
Trying to measure the levels of PO4 in the tank, for practical purposes, is a moot point. Evidently, the test kits most of us use only measure for inorganic PO4. Consequently, a low or nondectable measurement of PO4 by a kit can be misleading since you may still have excess levels of organic PO4 that feed the algae. I suspect this may be part of the probem in my case.
The challenge then becomes finding a balance of PO4 where where excess levels leading to algae problems are eliminated. According to Sprung and Delbeek, the primary input source of PO4 to most tanks is the food we add for the fish, corals, etc... Consequently, one direct way to reduce the PO4 load is to reduce the amount of food we add to the tank. In my case, and I suspect both of yours', this isn't practical unless we're going to get rid of some of the fish, corals, etc from our tanks. Otherwise, the reduced feeding might lead to starvation not only of the fish and corals, but also of the beneficial organisms we've established in our sandbeds.
A second significant source of the PO4 is the makeup water we use. This is one area where we can definitely make a difference. As mentioned before, in the near future I'm going to be moving up to an RO/DI unit which should help reduce any PO4 in my makeup water. Since I'm getting the unit for free, it's also an inexpensive option other than the cost of maintining the filters. I'll let you know how this works out. Particularly if I can get my wife to do a comparison test of my RO vs. RO/DI water.
Other options I found involve exporting PO4 from the tank. One that I'm in the process of trying is developing a deeper sand bed. Like you Rowdy, I currently have only a shallow sand bed. A 1/2" depth in my case. Dr. Ron S. and others advocate beds of several inches, which when populated with numerous organisms contribute to reducing detritious, therefore reduce breakdown of oragnics into readily available PO4. I've even talked to some reefers who have sandbeds as deep as 6.5" !! Gradually, over the period of the next couple of months I'm going to build up to approx. 3-4". Again, I'll let you know what happens.
Improved protein skimming also helps to reduce both forms of PO4. I currently run a HOB Red Sea Berlin located in my sump. Because of the cost, I don't see myself upgrading to one of the high end skimmers (Aqua-C, Reef Devil, etc..) anytime soon. So, until I win the lottery or I manage to sneak it by my wife, this option isn't availble to me
Adding a refugium, or converting a sump into a refugium, is another option. An external sand bed with macro algae can be used here to export a variety of nutrients including PO4. Here again, space limitions and a cost limit this option for me
Lastly, as alluded to before, there's the option of reducing the bio load of the tank by removing some of the fish, etc.. This would reduce the need for feeding the quantity I do, therefore reducing the PO4 introduced to the tank. I've gotten pretty attached to them, though, so this is a last resort. From a practical standpoint too, this isn't physically easy to do. The little buggers are quick to head for crevices and holes in the liverock when the dreaded net enters the water.
To wrap this tedious, rambling effort up, the spread of the wafer algae over the last several months has stabilized in my tank. Granted, it still covers 1/2 to 2/3 of the rock, but it's not progressing now. In fact, in a couple of areas, it has periodically receeded slightly. So, the import and export of nutrients including PO4 have evidently balanced out. Now I just need to implement ways to reduce the quantities and watch for the results. Given the fact that I've gotten used to the look of the algae and it's no longer spreading, I've got patience on my side. Now it's just a process of carefully monitoring visual changes in the tank as I proceeed.
HTH
Mike
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). I recognise the benefits of the DSB and I'm sure it will help in certain aspects, but doesn't it just aid in denitrification and not necessarily nutrient/PO4 removal? How does the DSB remove the PO4?
