110 point ORP drop after 10% H2O change???

[anothermineral]

Folks,

I performed my regular bi-monthly 10% water change the other day and noticed a drop in ORP from 390 to 280 immediately afterwards. The ORP level has remained in the 280-290 range since. The corals/fish look great. There are no observable issues with the tank.

I did not do anything different than any of the 100s of other water changes I've performed in the past.

Total system volume ~320G.

Any thoughts on what might have caused this?

Thanks

 

[Randy Holmes-Farley]

Was the probe exposed during the change? If so, how long?

It is common to have ORP drop when doing a water change,. The ORP is not especially high in new salt mixes, and is not usually any concern. ORP is not a measure of the purity or suitability of new salt water. Probably just a bit more Fe++ and a bit less Fe+++ in it, or some similarly uninteresting balance between redox active ions. It may take time to rise again.

Of course, the change may also have been coincident with, but unrelated to the water change.

This may be interesting to you:

ORP and the Reef Aquarium
http://www.reefkeeping.com/issues/2003-12/rhf/feature/index.php

 

[anothermineral]

Randy,

Thanks for the info.

The probe was never exposed during the water change.

It's doubtful that it was coincidental. The change was noticed immediately after the water change.

 

[Randy Holmes-Farley]

Has it come back up now?

 

[erikages]

I experience a drop of about 100 (430 down to 330) every time I do a water change. As Randy says, if it's simply due to the change and not a large dead thing somewhere, for example, you're fine.

Do you rodi your water? Regardless, orp drops.

My tank usually takes a day or two before it climbs back up to it's "normal" orp state (which the help of ozone, which shuts down again when the tank climbs above 400).

E

 

[anothermineral]

I use ro/di water (1 ppm tds).

The ORP reading is starting to come back up, but it's still down 80 from prior to the water change.

The tank looks great, no issues with the corals or fish.

 

[erikages]

ORP is always a bit of a mystery, but as Sprung and other writers continually point out, it's not what the probes are saying, it's what your tank is saying that counts the most.

There are some tanks with a "natural" orp of 150 all the way up to the high 400s and everything in between. Too, probes have memories of their own and can sometimes take days (weeks?) to "recover" from changes that affect them.

Sounds like your tank is healthy.

Curious: why is your rodi water 1ppm instead of 0? What tds is your tapwater to begin with? Where I live, I start with 12ppm tds, which I gather is unusually "clean" compared with cities in the 2 and 300s!).

Cheers,
Erik

 

[anothermineral]

erikages,

I'm jealous. 12 ppm out of the tap... back when I lived in NY, my goal was to get my RO/DI to 12 ppm.

In NJ, I have well water.

Out of the tap it's ~ 220 ppm. ~ 23 ppm after the RO stage and 1 ppm after the DI stage.

In my opinion, 1 ppm is pretty darn good. I don't replace my DI cartridges until I start reading 4 ppm. I've never had any problems with phosphate levels and my RDSB keeps my nitrates at 0.

 

[erikages]

Wow. I've heard of this. Makes me wonder why people in many places in British Columbia (Canada) bother with rodi at all -- by comparison at least.

Your water waste must be huge, but worth the effort given the tds levels you've got.

At my end of things I discard about 70% for a 30% return at 0ppm. I'm thinking of putting the discard into rain barrels for the garden, but haven't had the time.

You've inspired me to read up on tds a bit more -- obviously it's a general reference and water chemistry differs in areas and with different impacts on aquarium chemistry. Who knows? My raw 12ppm may have more detrimental effects than your 220.



Erik

 

[Randy Holmes-Farley]

In my opinion, 1 ppm is pretty darn good. I don't replace my DI cartridges until I start reading 4 ppm. I've never had any problems with phosphate levels and my RDSB keeps my nitrates at 0.

That could be a big problem with some types of tap water, especially if there is chloramine or silicate in it. Both of those (silicate and ammonia) will be among the first things released when the DI depletes and the TDS rises. They could be greatly enhanced relative to the tap water. When my DI depleted once, my limewater stank of ammonia from all of the ammonia flooding out of the DI.

That's why I recommend swapping to a new DI as soon as it rises to 1 ppm TDS (a new properly functioning DI should give 0 ppm TDS regardless of the input, at least until it is depleted).

This article has more:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

 

[Randy Holmes-Farley]

You've inspired me to read up on tds a bit more -- obviously it's a general reference and water chemistry differs in areas and with different impacts on aquarium chemistry. Who knows? My raw 12ppm may have more detrimental effects than your 220.

It might. I suggest focussing more on changes in TDS and getting to 0 ppm, rather than in looking at the raw numbers. Most of what is there is just sodium, chloride, calcium, magnesium, etc.

But if you passed RO/DI water at 0 ppm TDS through your household plumbing, the TDS would not likely rise above 1 ppm TDS, but there'd be a good chance of too much copper for use in a reef aquarium.

 

[erikages]

Does the rodi process get rid of copper?

 

[Randy Holmes-Farley]

Yes.