Nitrate not lowered by PWC

[minotaur]

My new SW tank is ready for fish. All I have to do now, is get no3 down to an acceptable level. My LFS said the a 10% pwc would do the trick.

I changed 3 gallons in the 29 gallon tank and no3 remained the same.

Should I do a larger change, or try a few more smaller ones? (It is a lot easier for me to do a 3 gallon change than it is for a larger one.)

tank stats before and after pwc:
nh3 = 0
no2 = 0
no3 = 50
sg = 1.023
temp = 80 deg f
pH = 8.3

thanks

[Hara]

How long did you cycle your tank, and when you did the water change, what type of water did you use?

[minotaur]

The tank has had no ammonia or no2 for about 2 weeks.

I used tap water, which was declorinated and sat out for 2 days. I also use Instant Ocean salt. Both of the lfs that carry lots of sw fish have said that our tap water is ok in our area.

[seaham358]

test your tap water for no3 and test the new sw for no3 . I would do a larger WC, you IMO a wc of 8-10 gals is fine.

[Fluff]

I agree do larger water changes. Test your tap water for nitrates as mentioned. Mine is loaded with no3 and doing regular large waterchanges with RO/DI water was the only way I could make a dent in mine.

[minotaur]

thanks, will check it tonight. If tap water has too much no3, i will try distilled.

thanks again

[Phyl]

I agree with the large(r) water change. If you change out 10% of your water and your trates started at 50 you're going to reduce them to 45. Well that's not much help. To get them to 10, for example, you'd have to do an 80% water change. If you want to go easiser on your inverts than that you could do a series of 3 40% water changes.

[malkore]

Well, 3gallons is about 10% of a 29gallon tank. That should lower nitrates by 10% assuming new water is 0ppm. That gives you 45ppm of nitrate...which would be hard to tell from 50ppm on any test kit I have seen.
Larger water change

[minotaur]

I tested the tap water...no nitrates.

I did a 25% pwc (8 gallons) and nitrates are still at or near 50. (as someone stated earlier, it's kinda hard to tell after 40 or so) If i do a series of (3) 40% pwc, how far apart should i time the changes? Can I do them daily, or every other day?

ps...one of my new small crabs bit the dust this morning, but the Scarlet Cleaner was very happy about the gourmet breakfast...

[krap101]

maybe theres something dead in the water that keeps adding ammonia, but since its cycled it turns into nitrates?

[Fluff]

I had this issue when I first set up my tank and it takes a while for the trates to fall when they are this high. I would do a water change every two or three days til you start to see a difference. Every change you do is diluting it a little, just keep at it.

[minotaur]

Could be, but would a small snail or crab have that effect?

Both of the large Turbo Snails are fine, as well as the shrimp and cucumber.

I will just try a bigger pwc...i need the practice anyway.

Thanks for your help everyone

[mjvincent]

PWC only dilute the nitrates. You have to do a LARGE change to have a noticable effect on the nitrate level. From there you should do a 10% (at least) weekly to keep nitrates down (until the bacteria develop to take care of the nitrates).