high nitrates

Dead wrasse?

 

Missing wrasse is what I'd look for first. 4 tds is not enough to mess up your nitrates IMO. 40 ppm is not the end of the world, just stick with good maintenance.

 

The only thing I can add is 4ppm TDS if the DI is exhausted might be enough to mess with the tank depending on what that 4ppm is and how much daily evaporation you have. I was fighting strange issues and noticed my RO/DI was at 6ppm - not a big deal normally, but I tested the RO/DI for phosphate and nitrate and had detectable nitrate (a couple ppm) and good amount of phosphate. With my tank in winter evaporating 2-3g/day that really added up fast in 110g total system volume since phosphate impacts the tank with small amounts!

 

FWIW in Iowa we typically have tap water that is very high in phosphate and nitrate depending on season - buy you probably knew that already! In a couple of places I have lived here 2 were river fed and 1 was well and the river sources were super high phosphate and nitrate from the tap. People in other parts of the country don't usually have such high phosphate in the water that we get. I think average Iowa river/stream water is 7ppm nitrate (you can see updated maps on the DNR site and it peaks in some areas at 20+) and average tile phosphorus was 0.5ppm (1.5ppm phosphate). So even small TDS in our RO/DI here can be trouble, not always, but something to keep in mind.

 

Any updates?

My $0.02 on the water quality is our systems are designed to remove 99% of impurities meaning the output TDS will rise in relation to the input TDS. Your water is testing 250 so an output of 2.5 is "normal" depending on what's in the 2.5 - 4.

I didn't see a reference to how big your tank is - depending on the size the missing wrasse may not have any impact to your environment, i.e. huge impact on a 12g and no impact on a 180g.

With your nitrates so high (40), what impacts have you noticed to your inhabitants? Nitrates at this level won't bother (most) fish but can impact inverts (snails) and cause sps to lose color - are you noticing any of this?

You mentioned that you've always kept your nitrates in check (15-20) after a 20g water change - this is a sizable change for most tanks which indicates you've always struggled with elevated nitrates and I'm curious as to what they are prior to these changes. The goal of most reefers is to keep nitrates <5 so you'll need to dig deeper for the root cause.

I just went through a similar situation with my 120g - nitrates raised to +/- 40 when I finally checked them. I don't know how long they'd been at this level as I've become complacent over the years in checking the basics such as nitrates.

I took a four pronged approach and recently things have cleared up nicely and I'm not sure what corrected the issue or if it was a combination of efforts:

Added an additional cartridge with catalytic activated carbon for chloramines which are high in Cedar Rapids. Theory is elevated chloramines cause die off increasing nitrates.

Changed water changes to small (5g) weekly instead of 20g per month.

Started carbon dosing - initially just vodka then moved to a vodka/vinegar combination to fight a subsequent outbreak of green hair and red slime algae from the vodka.

Moved an automated air freshener (Airwick) my wife had within 4 feet of the tank. My theory is this was the culprit the entire time and as it contaminated the water, it killed coral and snails which in turn elevated the nitrogen cycle (I just tested the end product nitrates).

-Eric