By Bob Goemans
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Bob Goemans corresponds with Douglas P. Milone (Charlotte, NC)

Douglas P. Milone (Charlotte, NC) writes...

Hi Bob,

I currently have a 180 Gallon Reef with an in the tank Plenum with 2 mm to 5 mm grain size sand and 4 inches deep. I also have a protein skimmer in the sump. As for livestock;

4 Square Anthais (1 Male others Female), 1 Royal Gramma, 2 Cleaner Shrimp, 1 Harlequin Shrimp, 2 Brittle Stars, 2 Serpent Stars, 1 Scopas Tang, 1 Algae Blenny, 1 Tiger Tail Cucumber, 1 Dragon Goby, 2 Acropora that are growing nicely, mushrooms, green stars, button polyps, a type of Cabbage coral and some pink soft coral that grows like a weed, looks like pink grass.

pH remains between 8.1 (night) and 8.3 (day), Nitrates and Phosphates I cannot get a reading on. I use RO water for make up and top-off and have 6 VHO 5 ft bulbs, and 2 Wave2K units.

The tank was set up 5 years ago. After taking about a year to build the inhabitants of the tank to where I wanted it, things were going great, with mostly purple and pink coralline, and many soft corals and mushrooms. I used to have colt coral that also grew like a weed, so much in fact, I was cutting it back, and using some fiberglass screen and some rubble to get it to bond to, then giving it to friends. Then about 2 years ago, with everything looking great, the pump on the protein skimmer got blocked up while I was away on business. I think a pink and black cucumber died that same week and we lost all the fish. I took about half a year to rebalance the tank and just let the corals grow out before I added any new fish again. All the corals looked great, then about 1 year ago I started getting a good growth of macroalgae and bubble algae which I tried to rip out (I also pruned the macroalgae, but left enough to keep it growing. Then about 6 to 8 months ago the bubble alga seemed to diminish but has been replaced by this much worse looking hair alga during the last few months, with the macroalgae growth seeming to slow and almost stop.

The current algae, is darker toward the bottom and lighter green at the ends. (See my photos, not great quality but gives you an idea) I rip out as much as I can each week and throw it out but I don't understand how so much biomass can be created. I'm not adding nearly that amount of food as I use to, but it seems to be as though its creating its own food source, much the way cyanobacteria does once its created its mat. Anyway, my wife and I have bought a new house and will be moving in very soon. We are only moving about a mile but I want to take advantage of the move. I'm thinking of pulling the plenum out and doing it separately in the sump, as I believe this is your recommendation for such an installation.

So with all that history, I'm really looking for your suggestions on how to take advantage of the move to re-establish the aquarium and get rid of the algae. This algae is very hard to tear off down to the roots and usually when I try to pull up pieces, some of the rock comes with it. I'm wondering if the algae could be the result of a failed plenum and that is why there are no readable nitrates or phosphates, or should I be looking at using different test kits? What seems odd to me is the Acropora over the last 2 years has tripled in size. Not sure if that's fast or slow, but it seemed pretty good to me and I took it to imply an overall good quality of water. One other odd thing happened during this time and that is the colt coral that used to be so prolific died off over several months, while other things were growing great.

I'm finally getting the ability to build my tank into the wall with its own maintenance room behind the tank and I want it to once again be the showpiece that it was, which means getting rid of this algae! If you had the flexibility of a 180 gallon tank, how would you set it up, how much substrate would be in the tank itself, 1 to 2 inches? Would you put the plenum on its own in the sump, how large should this sump be? What is the proper maintenance of the plenum? If I put it at floor level I won't be able to create a siphon to do any vacuuming. Is that required if it's just an open plenum? I assume you would recommend to continue use of a protein skimmer, and should I add a calcium reactor? I'm currently using a 2 part product.

Looking for any help or insight that you can offer, I'd rather not dump all the substrate and rock that I have now, but I'm willing to listen to any suggestions that you may have.

Thanks in advance for your time, it is greatly appreciated.

Douglas P. Milone

Charlotte, NC

Bob replies...

Hi Doug,

Thanks for your letter, and plenum systems are marvelous when properly set up and maintained! And thanks for the photos, as that helped with my detective work on this end.

Okay, lets back up and go back five years when you first set up the aquarium. It seems from your letter, the plenum worked very efficiently and water quality and animal growth was excellent until about three years later when a failed pump and a lost cucumber caused the system to turnaround and go downhill. What's missing from your letter is your general maintenance of the sandbed during those first three years.

I've had readers contact me and say LFS have told them never to vacuum the bed (in any type aquariums), as that removes too much food for the infauna and kills some of the bacteria living on the substrate. Of course, that's bad information, as the buildup of detritus is steady, and must be reduced through monthly vacuuming of all accessible sandbed areas. Keep in mind these are 'closed' systems! Furthermore, when the plenum is used in the main aquarium, 75% of the bed should remain exposed for maintenance! Not only does the bed need vacuuming monthly, but since the bed above the plenum grid has exceptionally fast growing bacterium, they tend to occasionally form cement-like chucks of sand that have to be broken up when found. Add to this some possible calcium precipitation, and these chunks of sand need to be broken up, as they block diffusion, reducing bed efficiency. Therefore, besides vacuuming monthly, the bed needs to be surveyed with a dull knife blade, e.g., butter knife, in a criss-cross pattern and when chunks are found, broken up with your fingers. If the bed is maintained like this, the plenum sandbed is unbeatable when compared to 'all' other forms of sandbeds!

So, lets say your bed maintenance did not go this road, and after three years of lacking proper maintenance 'and' an incident that triggered an organic nightmare, the overall system was ripe for the take over of unwanted alga. If so, I'm thinking you will find much of the present substrate bound together, especially if you have never surveyed it for blockage. Add to this, that the remaining loose sand is probably filled with detritus, and little filtration value of your sandbed remains. Then add the pump problem and animal die-off, and conditions were perfect for what you now have. And possibly this Bryopsis species of algae has made your aquarium a home, and like other forms of unwanted alga, can now make its own nutrients under its base thereby extending its existence even if the aquarium now had perfect water quality!

As for no nitrates and phosphates, I could believe that, as ammonium is the key factor that got the whole problem started! And that isn't going to be readily seen depending upon your pH level. But that is the key alga nutrient, with phosphate providing the energy needed. And if that phosphate were organic, then that won't register on your test kit. My preferences for these test kits are either those by Salifert or Merck. Furthermore, you want a phosphate reactor, or a canister filter as I do, to control phosphate. And my preference there is ROWAphos or the Warner Marine media.

What to do? If it were my aquarium and I was moving, none of the rock that had this alga would go into a new aquarium, even if it were scrubbed clean. Nevertheless, I would scrub that rock clean, sterilize it and let it dry out and possibly save it for use in a more distant future aquarium. But for now, get new, cured rock! As for the new aquarium, the plenum should be set up in an interconnected system, which should be about no less than one-third the size of the main aquarium. And if possible, contain no major bed obstructions. I should note I've used my interconnected plenums to raise sponges, as they don't need light, and are the best 'sponge' filters, as they filter tremendous amounts of water helping to produce even better water quality in your main system. The main system should have a shallow bed, about 1 - 2 inches of 2 - 5 mm sand. Again, leave wide-open areas to vacuum this new bed monthly, as detritus will continue to accumulate! And even if some bacteria are killed in the vacuuming, they will quickly reestablish themselves (a day or two, sometimes much less). And as for the plenum bed, which does not need a dividing screen, maintain as described above. And a 'quality' protein skimmer is a must! As for a calcium reactor, if you have had very good success with a two-part additive, the reactor may not be necessary. However, you should monitor your calcium and alkalinity and keep them balanced. As for installing a plenum at a height sufficient to vacuum the bed, my interconnected plenum in my 180 tank was only 6 inches above the floor, and that was sufficient enough to create a vacuum. But there is power assisted vacuuming equipment, but you'll have to search the web to find them.

As for the Colt Coral suddenly passing, I've experienced a similar situation a few years ago where I had a specimen not looking overly good. Resolved that by adding a good quality trace element additive.

In closing, I'm fairly sure you're going to need new rock and sand in your new system. And if your go with an interconnected plenum, its bacterium will very quickly form. Therefore, between the new live rock and the fast forming bacteria in the plenum bed, your now existing livestock should not have any problems in the new system.

Hope this helps and keep me posted. Visit my website at



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