Is there a correlation between phosphates and nitrate levels in water?


Hey Guys,

Is there a correlation between phosphates and nitrate levels in water? the reason why I ask is because I am starting to get some nasty hair algae. I was told by my lfs that it is a result of high nitrates and phosphates in my tank. I have been testing and testing...and more testing and all of my levels are at nitrates, no nitrites, no ammonia, etc. what should I be doing to solve the problem? although I am not exactly sure what my problem actually is...aside from the nasty hair algae...


What are you using to test your water? Some tests are unreliable....This is the first thing I would address...Most here on fishlore recommend the API Master test kit. If you would post your readings with an API kit, we can tell you if this is part of the problem. I know you said 0, but do you have fish in the tank? If so they really can't be 0.

The other cause of algae growth is high light, too many hours in the day. FOOD & LIGHT = ALGAE!!! Take either away, and the algae dies. Which can cause high phosphates, which can cause algae...

One method to control algae is to cover your tank, (pitch black) for 3 days, then make sure to do a 50% water change, and only use your lights NO MORE than 10 hours a day, in two 5 hour shifts with 2 dark hours in between.

One of the reasons some suggest not cycling your tank with fish food is just this same problem of high phosphates in fish food, it can cause algae problems.

What size is your tank, and what is it stocked with? We may be able to give you some suggestions.

Answer some of these questions, and we'll try to help more....Good Luck


HI davbrown79,
I feel your pain! "Is there a correlation between phosphates and nitrate levels in water?" Yep, if you want to grow hair algae, keep your Nitrates up and add some phosphates. strange that you have no Nitrates.. I have some q's
1, do you mix your water
2, how long has your tank been setup
3, is it stocked
4, what test kits are you using
5, how long are the lights on for? and how old are the globes?
You can get phosphate pads that you put in your filter,


ok...maybe I am stating things I guess I can prepare myself for all of the bad news and how I screwed everything here ya go

- I am testing with the API Saltwater Master Kit. It tests for high range ph, ammonia, nitrite, and nitrate using test tubes and dropping solution...and then comparing the colors to the is maintained at 8.2 and all of my other results match with 0 on the cards that are provided in the test kit

- as for the water...I purchase sea water from my lfs and purified water through a local water store...culligan or alhambra...something like that...

- my tank has been up and running for 6 or 7 weeks and is cuurently stocked with 2 ocellaris clowns, 3 chromis, 10 astraea snails, and 10 scarlet hermits

- for lighting I have 48" t5 ho nova extreme with 4 lunar lights...216 watts...2 460 nm actinic bulbs and 2 10kk bulbs. I run them from 7 am until 7 pm...I start with the actinic bulbs for 30 min in the morning and then kick on the others...and reverse the order at night

- as far as feeding...I feed brine shrimp every other day

I think I answered most of your questions...I hope that this helps...thanks!!


You haven't said how large your tank is. Calculate the watts /gallon, and compair with what you have your tank stocked with. Corals? anything that ablosutly needs high light? I'm not a saltwater person, but it sounds like you have fairly high light, and run it at least two hours longer than I would if I was trying to cut down on algae.

Hope some saltwater people jump on soon to help you out....


my tank is 55 gallons and I am also using a sump...


The lack of Nitrate readings.. you should be getting a reading of Nitrates...
Lights on for 12hr will be adding to the hair algae problem, try to have them on for only 8-9hrs max. now for the fun bit.. start removing the algae, pinch it between your finger and thumb, and remove it.. the hair algae needs light and food to grow, so cut down on the lights to start with and start ripping the stuff out.
May pay to get the water tested at the LFS.. to check on the Nitrates..
You are running a Skimmer?


why should ibe getting a reading of Nitrates? what should they be at? I will cut down the light like you said and I'll start removing the algae...that sounds like a blast!! I am running a protein skimmer and seems to be removing lots of nastiness...


Ok, I am a very slow typer, so I have a link for you.
Click on "THE STABLE" and then read the bit on filtration and water


Some of this has already been said, but just to pull it all together...

Algae needs light and food to grow. Both nitrate and phosphate can provide the nutients it needs to thrive. Both nitrate and phosphate can come from multiple food and tap water being a couple common ones. To get a handle on your algae problem, you need to figure out what factor(s) are at play in your particular tank and address them. I can identify one issue for you...You have strong lighting, which is good if you plan on keeping corals. However, 12 hours is too much, IMO. I run my lights 7-8 hours a day. My corals are fine, but algae is under control. Whether or not phosphates and/or nitrates are an issue in your tank can only be answered by testing. I know you are testing for nitrate already, so I will come back to that in a sec. Phosphates are sometimes added by water companies to municiple water supplies. It can also come from some sw additives and even from salt mixes. Be sure anything you add to the water does not contain phosphate. Sounds like you are feeding sparingly, which is good. While you are working to get the algae under control, you might even want to fast your fish for 2-3 days. Don't worry about that...they can go longer with no food, so they will be fine. Get yourself a phophate test and see where you are. You may be in for a shock. Back to nitrate. Are you being violent with bottle #2 when you do your nitrate test? need to shake the bejesus out of it, even rap it on a hard surface a few times before you use it. Otherwise you will get bad results. Unless you have some chemical filtration, a large amount of some kind of macroalgae in your system to absorb nitrate, or an anaerobic bacteria bed (deep sand bed or something similar) you should be getting some sort of nitrate reading. The end result of the nitrogen cycle is nitrate, so it has to be there unless something is absorbing it from the water. To answer your question on what should the reading low as you can keep it. Inverts are sensitive to high levels of nitrate, in addition to the algae concern. I am trying to get mine down below 10 (and having a heck of a time of it, I might add).

Anyway...this is getting long...look it over and see what questions you have and if anyone else chimes in with some ideas.


ok...thanks for all of your input...I apologize if I ask ridiculous questions over and over, but I just want to make sure that I do things right...the last thing I want to happen is have my tank littered with dead critters!

I forgot to tell you that I do have a green mushroom and some bristle worms in there as well

I will go ahead and fast my fish for the 2 or 3 days and then get a phosphate test.

would 1.5 - 2 inches of live sand be considered an anaerobic bacteria bed?

as far as shaking the test solution, I thought I shook it well enough...but if you're saying to shake the bejesus out of it...I haven't shaken it that hard...I will shake the snot out of it tomorrow when I test the water again

so it seems to me that something is obviously out of whack...most likely with me and I need to figure out what it is...thanks...i'll let you know my results tomorrow night


Don't the grand scheme of things, hair algae is not a serious issue. Your tank and inhabitants are not in danger. Just work the problem and eliminate potential contributors, one by one, until you find the issue (or issues) causing it. How much hair algae are you looking at? Any pics?

No, 1-2" of substrate is not deep enough to establish an anaerobic bed. You need more like 4-5" for that. If you are thinking of going that route, though, research DSB (Deep Sand Bed) thorough before actually doing it. There are potential pitfalls (like a sudden release of poison into the tank) and you need to really know what you are doing so you do not set yourself up for a more serious problem.


well tonight I am going to redo my tests again and see where I am. in terms of how much is covering my rocks a bit heavy in one particular area...I want to say it is about 1/4 in. in length. when I get a chance I will post pictures. I plan on scraping it off tonight with my fingers...can I use a toothbrush on that stuff to help? DSB for thanks!


"can I use a toothbrush on that stuff to help?" No brush.. just plucking..little bits that get loose in ya tank can spread.... and anyway, its no fun if you do it the easy way!
Get ya water right, and ya lights, keep plucking and you will have it licked in no time..
3-4 weeks tops...

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