Help with Nitrate test kit from Redsea reef test kit

[babycover]

Below are 2 nitrate test from the same tank using Redsea reef test kit combo.

Frist one is 5ml tank water which show nitrate level wouls be equal or more than 50ppm.
Second one is 1ml tank water with 4ml RO water, show nitrate level around 3ppm x 5 = 15ppm.

Can i please have some advice why the teat kit show different figure?
Did 2 times water changes, each 20% and 2 weeks apart, still yeild the same result.

Can I please have some help!!!!

Tank is 2 months old, cycle with DrTim.
Reef rock purchase from LFS. No live rock.
Sand from previous tank owner but I washed with RO water.

Water parameter :
Ph 8.2
Salinity .025
Amonia and nitrite : 0
KH : 9dkh
I didnt have the test for calcium and phos but my LFS use API test kit which show me similar parameters but with Nitrate 5ppm and Phos 0.2

Live stock :
2 clowns only fed once a day and make sure they dont have food left over on sand bed.
Frog spawn
Hammer
Acan
Blasto
Duncan
2 colony of rasta Zoa (fist size)
Xenia
All corals are open up nicely, Duncan got 4 new branches whithin a month.

CuC: 2 trocus, 2 nassrius, 2 snails with trunk which i forgot the name

Sump :
Aquaexcel skimmer run 24hrs
Refugium with chaeto and amphipod
Some marine bioball

 

[AllSignsPointToFish]

How fast is your macroalgae growing? i would think that with 50 ppm nitrates, you should be covered up in GHA in the display tank.

 

[babycover]

Interestingly all i got is a brown film algae on the glasses which i clean every week when do WC. Notice some green coraline (maybe) on the rock but that about it. No other algae spotted.
my chaeto grew a bit but definitely not huge in comparison when i first got them.
hence i have no idea why the test kit show different resu

 

[zapbap99]

sometimes those testkits dont read accurately but i mean if your corals and stuff are thriving i see no need to forcefully change it fast.

 

[Therinx]

I've gotten the same 50ppm reading vs. diluted reading like you from the Red Sea test on multiple occassions and at this point and couldn't figure it out either. I kept thinking maybe i didn't put a full 5ml in the tube, or didn't clean the vial properly, but it kept happening.

Try a different test kit brand to compare or bring a vial to your LFS and have them test, just confirm whether your test kit is functioning properly.

 

[AquaBiomics]

Nitrate tests are affected by sodium concentration, aren't they? If so RODI would skew the diluted reading.

 

[babycover]

sometimes those testkits dont read accurately but i mean if your corals and stuff are thriving i see no need to forcefully change it fast.

Ye, but i wanted to get the parameters down so i can start putting in SPS

I've gotten the same 50ppm reading vs. diluted reading like you from the Red Sea test on multiple occassions and at this point and couldn't figure it out either. I kept thinking maybe i didn't put a full 5ml in the tube, or didn't clean the vial properly, but it kept happening.

Try a different test kit brand to compare or bring a vial to your LFS and have them test, just confirm whether your test kit is functioning properly.

Oh i see. Glad to hear that im not the only one has this problem. LFS used API test kit and as far as i know, it inaccurate so im not sure. But ye LFS got only 5ppm which make it much more confusing.

Nitrate tests are affected by sodium concentration, aren't they? If so RODI would skew the diluted reading.

I'm no chemist haha wish i pay more attention in high school haha. Hoping to get some advices from the smart people up here