[jed42]

Should I be testing my phosphate level. I currently test for: ph, nitrate, nitrite, cal., am. Live stock and test results look good but I'm hearing, "check your phosphates." I have a AG 65 gal. SPS, LPS and a couple clams, tank cleaners and 6 fish.

Jed,

[Ninong]

Well, let's put it this way, you could test for a lot of things. Most phosphate test kits aren't all that sensitive on the low end to begin with. If your phosphate is above 0.03 ppm, then it's too high. If you want to test for phosphate, go ahead. I did test for it from time to time but I never did get a reliable reading. Hopefully that was because my phosphate level was extremely low.

If you're concerned about phosphate, run an iron-based phosphate sponge product in your sump.

You need to test for calcium, alkalinity, magnesium, and nitrate. You don't usually need to bother with testing for nitrite or ammonia in an established aquarium, just one that is very new. You might want to test for ammonia and nitrite if you think something rather large is missing in action and may have died somewhere inside the live rock where you can't get at it.

If your calcium and alkalinity are fine, then your pH will be fine. Check your magnesium often enough to make sure it isn't falling on you.

[jed42]

That's good info thanks. I use RO and it's .30ppm and I understand phosphate is from bad water. I haven't done a mag test but I add a mag additive weekly. What do you think about doing that? Are should I invest in a mag tester?

Jed,

[Ninong]

Phosphate comes from a lot of different sources. It's sort of part of life at every level. It's certainly in the foods that you feed to the tank. It could be in the water but R.O./D.I. usually removes most phosphate. I wouldn't get too worked up over phosphate unless it starts to get really out of hand.

You really shouldn't add anything to your tank unless you have tested first and discovered a need for it. So, yes, you really do need to get a magnesium test kit. I used Salifert. I believe it was probably reliable.

If you are doing frequent water changes (say every two or three weeks), it's possible that your magnesium levels are fine. You really don't know if you don't test. NSW Mg = 1285 ppm, therefore you want to be somewhere between 1200-1500 ppm Mg. Right around 1300 ppm is considered ideal by most people. You have a problem if you let it fall below 900 ppm. Low Mg makes it difficult to maintain proper Ca levels.

[ChrisP]

Does it make sense to run phosphate removal media 24/7, even if your tests are negative?

[Ninong]

If the test result shows no phosphate at all and it's a trustworthy test, I would only run a phosphate sponge product if I had problems that are either directly or indirectly related to phosphate. Remember, there is always phosphate in your tank just as there is always nitrate in your tank. It's just a matter of how much and whether it registers on the test. Not all tests are created equal, some are pretty useless.

For example, suppose you have a problem with cyanobacteria. It's photosynthetic and it's nitrogen limited but you can still mess with it if you can get the phosphate down below the natural 1:16 ratio* with nitrogen. When you have any of the various 'nuisance' problems, it's always a good idea to try to get everything under control, including phosphate, whether it shows up on the test or not.

Bottom line: If you have no problems remotely related to phosphate and phosphate doesn't show up on test results, don't worry about it. Otherwise, worry about it.

*C:N:P = 106:16:1 -- That's the Redfield Ratio for phytoplankton and it apparently holds true for cyanobacteria to the extent that if you get the phosphorus down below the 1:16 ratio with nitrogen, you interrupt the cyanobateria's ability to photosynthesize. That's apparently why some hobbyists have no cyanobacteria even though their nitrate levels are not all that low and others have cyanobacteria with nitrate that is barely measureable.

Diatoms need in addition to other nutrients silicate for their cell walls and the proposed Redfield nutrient ratio for diatoms is C:Si:N:P = 106:15:16:1. You can control diatoms by getting the silicate down.