nitrate issue

[Ksmmike]

I'm at a loss. I have a 120 gallon tank with 10 fish. The tank is about 18 months old. I had kept close eye on my parameters and did water tests every week. I was doing changes every week early on and later every 10 days or so. I had low nitrates, barely registering and barely any phoshates, usually showing zero. So I stepped up with more feedings and turned off my skimmer for a couple hours a day. I had a tad of GHA before and now nothing.

I went on vacation early in June (8 days, the skimmer stayed on all the time I was away) and when I returned the nitrates were over 40. They got even higher, off the chart after another few days. I began doing water changes every 3-4 days. I've done 5 in just under 3 weeks since I returned and the nitrates wont budge. I began using Red Sea no pox and still the nitrates wont budge.

Nothing that I can see has died except maybe a shrimp while I was away that I no longer see popping his head out. I haven't added anything or changed the fish food. I change 20 gallons of water during each water change. Some of my acros are losing color and one has died off. I need to get these nitrates down but I have no clue where its coming from. Ive been away before and this never happened. The person who watched the tank was given a list and she claimed to have followed it closely. She watched it before and I didn't have this problem.

Do you have any ideas or suggestions?
thanks
Mike

 

[Ling_Thing]

Sounds like a faulty test kit, I can usually
Look at my acros and see where my nitrates are if I know what the alk is. Have you tried a different n03 test kit? Nopox absolutely demolishes nitrates so that’s why I’m suspectful of your test kit.

 

[Ksmmike]

I can test my other tanks and the test kit says there is little nitrates. My alk is about 8.7 where I try to keep it. I make my own water and changed the filters just to be safe.
It runs at zero tds. I checked the salt after mixing and it runs at zero nitrates using the same kit. I wish it were the test kit, but I don't think it is. I would have thought doing several water changes would have knocked them down some along with the nopox. I'll buy another test kit, but like I said, it seems to work fine when I test other things.

 

[lapin]

Provided you have high nitrates: Carbon dosing can take a few weeks to become effective. Bacteria need to grow. It takes time. You build the dose over time as you dont want a bloom . Sometimes if you have next to no phosphates, that can cause nitrates to not go down.
I would do a 40 to 50% water change and measure the water right after the change. Nitrates could be bound up in your rock and they have finally hit the point of not being able to absorb any more.
These are my ipinions