Nitrate/Phosphate problem

[rjs5134]

Granted my skimmer stinks and desperately needs to be replaced, but I think something else is wrong. I use Instant Ocean salt mixed with filtered water from a Spectra-Pure RO/DI filter. The inline TDS meter reads 0ppm on the product. The unfiltered tap-water shows small quantities of both nitrates and phosphates, but the filtered water reads 0 with both Aquarium Pharm and Salifert test kits. The tank water also reads 0. I've been doing a 5-10% water change twice per week and a 25% change about every other week. In lieu of all this, I still have a MAJOR cyano outbreak. While on vacation the first week of August, the temperature in the tank exceeded 90 something degrees and killed nearly everything in the tank. Is it possible the former life within the rock is still creating a nutrient problem? I would expect after nearly 11 weeks, this would begin to subside. With every water change I try to remove as much of the unsightly cyano that I can, but it comes back with a vengeance. I guess the question is how long can a major die-off in the LR cause this problem?

[Ninong]

Sure, it's possible that you're still experiencing dieoff from the August event but not very likely.

There are so many different triggers for cyanobacteria that it's virtually impossible to pinpoint exactly what the cause might be in a particular tank. All you can do is try to eliminate the potential causes and hope that things improve. Besides, unless it gets really, really out of hand, it's not the end of the world as we know it.

First, consider your lighting. Are your lamps in need of replacement? If so, change the lamps. Cyanobacteria is photosynthetic and changes in lighting -- specifically a shifting to the red end of the spectrum -- can trigger an outbreak.

How about your calcium and alkalinity numbers? Are those where they should be? Try to keep calcium close to 450 ppm and alkalinity around 10 dKH. I like calcium in a range of 425-475 ppm myself and alk between 10-12 dKH. As long as you keep the calcium above 400 ppm and the alk above 8 dKH you should be OK but there's nothing wrong with going a little higher on both.

What about water flow in the tank? Do you have good water movement? Cyanobacteria doesn't thrive in strong water current because it breaks up the strands. Making sure that the water current across the sandbed (if you have a sandbed) is adequate is important in eliminating cyanobacteria.

Is your skimmer working properly? Make sure it's cleaned on a regular basis and working properly.

How are you maintaining calcium and alkalinity? Are you using a calcium reactor or do you dose Kalkwasser? Dosing Kalkwasser (limewater) helps to control phosphate. Cyanobacteria requires nitrate and carbon dioxide to thrive but keeping phosphate very, very low helps in that it upsets the ratio of calcium to phosphate (16-1) and interferes with the processes involved in the proliferation of cyano.

You might want to consider running both carbon and an iron-based phosphate adsorbing media to see if that helps. There are several phosphate sponge products that are iron oxide hydroxide based. Just put a cup of that in a mesh bag and place it in your sump. Same with the carbon. See if that helps.

Cyanobacteria can also be triggered by changes in water temperature. In fact, almost anything that changes the previously existing equilibrium could potentially trigger cyanobacteria. It's ubiquitous; it's just waiting for an opportunity to thrive.

[rjs5134]

Wow, that's a mouthful.

Lighting should not be a problem. I replaced my previous Coralife PC fixture in July with a 2x250w 10,000K MH and 2x96w PC fixture.

Calcium and Alkalinity have almost always been above 400ppm & 8dkh. I haven't checked recently, but since the crash they've ran on the high side. To maintain the levels I use Kent Marine Calcium, Strontium & Molybdenum, Iodine, etc. all in liquid form as per the instructions and as needed according to test results.

Water flow could be an issue. I have the main outflow and a Seio 820 so it's pretty good, but the ugliest area of the outbreak has long strings floating up. Guess I should adjust the Seio and see if this helps.

The skimmer works properly when cleaned. I seem to be doing this about two or three times per week. It still isn't sufficient and needs to be replaced, but thought I could put this off with frequent water changes. I will be replacing the existing sump with one made from a 29 gallon tank which would allow more room for a larger(& better) skimmer. Guess I have to do this sooner than later.

In the interim, I'll add a phosphate sponge and continue with the water changes. Thanks for the ideas Ninong.