Nitrate level after 60 gallon Water Change

[Canan]

I need some help/support from experts here, am little bit confused.

I have done 2 water changes in the last 1 week (30 gallon each) and was expecting a good change on my nitrate levels. At the first change, it dropped to 80ppm from 160ppm, however after the second change the nitrate level stayed the same.
The tank is sized as 180 gallon, however after subtracting the volume of the live sand and rock, I am assuming the net water amount should be around 120 gallon.

Below is the detail of my live stock and the test results.

I am using the API Reef and SaltWater Test Kits.
Expecting a good amount of nitrate decrease should be normal after these water changes,isn`t it?
Need some advice on what can be the reason for the stable nitrate levels?

Thanks in advance...

 

[Ocelaris]

You could easily have nutrients bound up in your sand or other places in the tank. At best water changes will help for a very short time. Long term, look at your nutrient export methods. Chaeto and a cheap led grow light are very effective if you haven't looked at a bigger skimmer and more regular cleaning of the sand etc...

 

[Big G]

How long did you wait to test after the first water change?

 

[Canan]

How long did you wait to test after the first water change?

I have done the tests the next day (gave 24 hours for the water to circulate and mix)

 

[Canan]

You could easily have nutrients bound up in your sand or other places in the tank. At best water changes will help for a very short time. Long term, look at your nutrient export methods. Chaeto and a cheap led grow light are very effective if you haven't looked at a bigger skimmer and more regular cleaning of the sand etc...

I haven`t done sand cleaning yet. I am simply pumping out the water from the low levels of the tank with a simple submersible pump.
My lighting fixture is Coralife LED Aqualight-s, 48'' 1400lux Par@12. I have 2 of this installed and running 6 hours every day.

 

[Randy Holmes-Farley]

Actually, within the precision of a typical nitrate kit, I don't see any issue and there's nothing special to try to explain. You should not assume high precision to this type of test kit where the color card shows big jumps between levels .

A 30 gallon change in 120 gallons total drops things to 75% of the starting level.

Expected change: 160 ppm --> 120 ppm ---> 90 ppm
measured change: 160 ppm --> 80 ppm --> 80 ppm

 

[Canan]

Actually, within the precision of a typical nitrate kit, I don't see any issue and there's nothing special to try to explain. You should not assume high precision to this type of test kit where the color card shows big jumps between levels .

A 30 gallon change in 120 gallons total drops things to 75% of the starting level.

Expected change: 160 ppm --> 120 ppm ---> 90 ppm
measured change: 160 ppm --> 80 ppm --> 80 ppm

Hi Randy
You are absolutely right. It is quite possible that I am off reading the color chart or test kit (API) is not responding good enough at high level of nitrates.
I would do 2 more water changes and share the results here again.

Thank you so much!!!

 

[Big G]

Agreed ^^^ It always amazes me how much water you need to change to lower nitrates down to a "comfortable" level. You end up usually at about 100% of the water being changed out, and in your case, at 30 gallon increments.

 

[Canan]

Hi All,
After doing three more water changes (each of 30 gallon, a total of 150 gallon), the nitrate level is somewhere between 5-10 ppm (as per the API test kit).

Thanks for all your help @Randy Holmes-Farley , @Big G , @Ocelaris

 

[Randy Holmes-Farley]

You're welcome.

Happy reefing.