Nitrate- cannot get it to fall

hrdneglcry · 2026-09-18T18:59:39-0400

Hi,
Never tested for nitrates before. But when buying non reef safe hermits I noticed they'd die after 2 days. I have two groupers, a damsel and a blind trigger in the 180. I think the nitrates caused the blindness and the other Niger Trigger to die. This tank has been running for over three years. It has a 120, 3 chamber sump. Hundreds of pounds of live rock. 3 aquaclear 110s, a Reef Dynamics skimmer. Two almost 3 foot mangroves in the sump. Aragonite bottom.
So I changed around 100% of the system and still the nitrates were high. I tested the tap water and it was the same amount of high nitrates. But a week later it was ok. But still nitrates in the tap. I use an Aquatic Life four stage RO unit. All of the filters are new. I have changed over 100 gallons with RO water and this picture is the current nitrates. If I vacuum the sand no brown comes out at all. Its the very fine Aragonite.
This is my tank today with the 120 sump with LR.
Hair algae problem for awhile. Changed lights. Working on Briopsis problem.

ShakeyGizzard · 2026-09-18T19:36:00-0400

Don't look through the side, sit it on the chart and look down through it., I ditched the Aquactic life, and went with a BRS 4 stage, cheaper in the long run, as long as you back flush your RO filter. the filter changes are under $25. Maybe use some distilled water for the next few water changes and see if that helps get them down. I use Dollar General distilled water for my Phyto.

DmitryB · 2026-09-18T19:53:57-0400

Paging @Randy Holmes-Farley #reefsquad

EnterName · 2026-09-18T20:00:08-0400

When looking through the side of Salifert's NO3 test you have to divide the reading by 10, so look from the top if you need to get readings above 10ppm.
Even 50ppm are within Randy's nutrient target ranges and absolutely safe for fish and corals, so I don't think this caused any of your livestock to die.

Randy Holmes-Farley · 2026-09-18T21:18:50-0400

Many tanks have 100+ ppm nitrate without apparent issue.

I’d urge consideration of other issues.

JonasRoman · 2026-09-19T05:00:58-0400

I disagree about optimal nitrate levels. Research shows negative effect on respiration, oxidative stress of corals already at quite low levels. See link.

My feeling and experience is that tanks with nitrate above 20 have in general more issues. For me I would say10-15 ppm is a max level. Think of the natural reef where we have 0.5 ppm ish(or lower)

Anyway, here I wold say you need more anaerob area to favourice denitrification.
Try to by 3 pc Maxspect denitrificaction blocks. They work. Includes a local carbon source. Takes a few months to fully work.

https://www.nature.com/articles/s41598-020-68916-0

Jonas