Water parameter question

[reef tank 2.0]

Maybe I can get some other insight on my nitrate level issue, and what's going on in my tank. I am kinda confused.....

My tank has been up and running for a year and 3 months. I have a 130g tank, with a 40g sump.
reef octopus 200-INT skimmer
2.5" deep sand bed
weight of rock unknown

I don't know when my high nitrates began, but I have been fighting them for as long as I can remember. Since the beginning, I was doing 50 gallon water changes every week. As you can imagine, that got costly and I was flying through buckets of salt rather quickly. Not to mention all the water I was using in order to do so. This was weekly, and went on for roughly 2-4 months, if I recall. During all those water changes, my nitrates never dropped. From what I tested, they always ranged from 60-90, but again, it was based off the color chart. I was getting worn out with the cost, as well as the manual labor of doing these water changes. After talking to a couple reefers, they recommended that I stop for awhile. The tank was really new, and that I wasn't leaving it to do it's thing. Let it go, and see what happens. So I did. I stopped the weekly changes.

I quit stressing about it and changed the water changes to weekly, but only changing 25 gallons a week. This didn't last very long, since I never saw any change in the nitrate levels. So I yet decreased even more. I then decreased the changes to bi-weekly, doing 50 gallons at a time. I have been doing that for the last few months. During the last couple months, I think my feeding habits were part of the issue. I was feeding twice a day. I have stopped that, and now feed once a day. I've been sticking to that routine. No one seems to be starving. Nitrates never leave the 50-75 mark, Ever. I mainly do water changes now to replenish the Calcium/Alk/Mag levels that my corals have used up.

I don't have room for any more storage for water bins, or I'd do one large change and hope for the best. So the 50 gallon change is all I have room to do, for now.

So here I am 15 months in, nitrates are stupid high, but yet I have lost nothing due to them. Let me rephrase, I lost some corals a while back, but not sure why. So I can't say the high trates were the issue.
I have read that one with high nitrates will have algae issues, unclear water, brownish coral, and dying coral at that. None of which I have , or have had. Correction, I have had diatoms and cyano, but that was it. But that was due to the new tank syndrome. I had weeks of diatoms, but I have been lucky to not have any more break outs of anything. But my tank has been clear for months now.

If I have very high nitrate levels, and my corals are, or should be struggling.......then why arn't they? I mean, I have never had a salt water tank to compare it to. I don't know if my corals are growing at a normal speed, slow speed, or fast. If it was up to me, they arn't growing fast enough . But none are changing colors that would raise a red flag. Maybe I have hardy corals that don't care as other corals might.

Here are my corals and parameters:

Acan
Chalice
Montiporas
toadstool
frogspawn
duncan
trumpets
open brain
stylo
hammer

Ammonia - 0
Nitrites - 0
ph - 8ish
nitrates - 75
cal - 400
alk - 8.3
mag - 1350
phosphates - undetectable
temperature - 79

livestock
(2) chalk bass
(2) percula clowns
(2) fire fish
(1) starry blenny
(1) yellow coris wrasse
(1) tomini tang
(1) randals goby
(1) red serpent sea star
scarlet hermits
snails
(1) tubeworm
(3) peppermint shrimp

If you have made it this far, after all that reading, I thank you. But if you could chime in and tell me your thoughts, I'd appreciate it. I don't know why my tank seems very healthy, when the nitrates say otherwise.
I have not done any dosing or extra things to get the trates lowered. Only water changes and reduced feeding.

 

[dyazdani]

What test kit(s) are you using?

 

[reef tank 2.0]

Sorry, forgot to answer that...I knew it would come up

I use Salifert 100% of the time

And some more info:

I run GFO, as well as Carbon
My sand bed is Caribsea Aragonite

 

[bertoni]

If there's an underlying issue, water changes seldom or never help to reduce the nitrate level for very long. Tanks can produce a lot more fairly quickly. I see that the nitrite level seems to be zero, but nitrite can confuse nitrate test kits, and I might get a second opinion on both results, if that were easy. I suspect that the kits are fine, but we do see failures.

If everything is doing well, you could ignore the nitrate level. Otherwise, there are lots of approaches to consider. If the tank has a substrate that's trapping detritus, that can be an issue. I had to ditch my crushed coral and the like for the finest grade of sand. Artificial filtration media, like bio-balls, seem to be able to increase the nitrate level in some systems.

The most common issue is too much food for the filtration system to handle. Better skimming or more live rock can help, as can carbon dosing (adding vinegar, vodka, or the like).

If you like the way the corals look, leaving well enough alone might be the best approach. The fish won't care at all about the nitrate level, not until it's much, much higher.