Visible change in corals, significant ORP drop

Cas8100

New member
Hi All,

I am hoping for some input from the community on a problem that started yesterday afternoon. My tank is an Innovative Marine AIO Fusion 40 gallon. I use a Reef Octopus HOB skimmer. This is our first venture into a reef tank so we are still relatively new. I have separate 40 gallon jugs in the basement beneath the tank (one for fresh RO/DI ATO and one for replacement salt water - mixed using Instant Ocean Reef Crystals). I do a daily 1/2 gallon water change, which results in approximately 40% water change per month. Tank is running under a Kessil A360WE.

The tank has been running for a little over six months with no problems whatsoever. Water parameters have been incredibly stable, with very few tank losses.

Now start yesterdays problems. Around noon I was doing some cleaning and did our daily water change. The water immediately clouded up and our star polyps got this really weird look. Almost burned. They got a brownish color and looked like wilted flowers. Within 30 minutes, every coral we have in the tank had wilted or closed. In the back of my mind I knew something wasn't right, but attributed it to the fact that I had just stirred a bunch of stuff up.

Getting up this morning, most of our coral still looks closed up - certainly not healthy. So I dig into the Apex and take a look for clues. At the instant I did the water change yesterday, the ORP dropped from around 400 to 270. So I get online and see that a dead animal can cause significant (and instant) drops in ORP. We just lost a sizable Cowry a couple days ago and his shell had been sitting on the sand bed. Maybe, that was it, maybe not... So I do another 1/2 gallon change this morning and we get another significant drop to around 210 ORP. Both times, the water clouded up immediately upon adding the new mix and cleared up within about an hour. The mix in the reservoir is about two weeks old. I've had no problems using it up until yesterday.

The water parameters all look normal, with the exception of the new salt mix ORP. It's tough for me to understand how a 1/2 gallon (or 1.25%) water change can cause such a large drop in ORP.

Tank
Ammonia - 0.0
Nitrate - 5 ppm
Alk - 10
PH - 8.15
ORP - Normal 400, After water change yesterday 250, After water change today 215
Ca - 583 ppm

Salt Reservoir Downstairs
Alk - 11
PH - 8.20
ORP - 205
Ca - 600 ppm

The only other variable is that yesterday was the first day running a new water pump that is used to fill the tank with new salt water mix. I used a very small amount of the waterproof PVC glue to fasten the flex tube to the pump (very small amount). I also didn't rinse the pump in water before dropping it into the salt water reservoir (maybe was a poor decision).

Can anyone shed some light on what might be happening here? I'm trying to decide if I should drain my entire salt water reservoir and make a new mix. Alternatively, bad salt? Other type of contaminant in the reservoir - perhaps from PVC glue? Or maybe just me overreacting to some type of natural occurrence?

Thanks for any thoughts from the expert community!
 

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I've heard though that low ORP can be normal for brand new salt mixes? If that's the case, a large water change might exacerbate the issue. I guess if that was the case though I wouldn't have been able to use this batch of water for the previous two weeks without any issues.
 
I mixed 10 gallons of new water..... Haven't put in the tank yet. It is measuring ORP at 200 and pH at 8.3. I threw an air stone in the tank hoping that if the CO2 / O2 levels were out of whack it would help balance things out.
 
What kind of salt are you using?

Is the nsw coming out of the reservoir cloudy?

Take a sample of the nsw and do some tests on it. Alk, NO3 and PO2. As well as NH4.

I wouldn't necessarily chase ORP numbers. But a sudden large drop like that usually means something changed.


Sent from my iPhone using Tapatalk
 
Vincent -

I'm using Instant Ocean Reef Crystals. Of course yesterday's event happened right before I had to leave my tank to run on autopilot for a week so I won't be able to get all of those measurements. Things like this only happen when I'm leaving town...

Before leaving, I mixed up 10 fresh gallons of mix and measured the pH at 8.3 and ORP of the new mix at 200. I know that ORP is essentially a useless measurement, but I was curious what the value of the new mix would be. I've previously measured fresh mix with calcium running near 600 and alk between 10 and 11.

Since leaving the tank alone for about 24 hours, the ORP is slowly climbing back up - Currently at 224.

At this point, I have no idea what happened. I'm hoping by the time I return home the tank will be back to looking normal. Every parameter I've tested seems fine. The only thought I had is that my salt reservoir hadn't been mixed heavily since the initial mixing about two weeks ago. I changed the mixing pump schedule to ensure that the reservoir gets four hours of mixing a day instead of only being mixed just prior to use. Perhaps the lack of mixing motion has caused some imbalance in O2/CO2.

So for now, I guess all remains a mystery. I'll post back in a week or so if I have any repeat events or if I can find any causes.
 
You probably lost both oxic and anoxic bacteria by stirring stuff up. These deaths are most likely minor and will settle down quickly, but they can cause a quick mini-cycle. Even though nobody wants to hear this, a six month old tank is still not the cycle-factory that a more established tank is and your bacteria base is probably not what it will be in another six months or a year, so it ends up being more extreme now.

The other thought is that your smallish water changes could be somewhat toxic with salt that settled. Salt mix needs to be dry stirred before being used in small quantities or you can end up with too much of this or too little of that. This is any salt. I like to mix a whole bag of IO at a time to avoid this, but this makes 44G which is a lot for you. The 600 PPM of calcium is a LOT, even for RC which leads me to believe that the mix was not uniform - most folks get 490, 13 and 1440.

My guess is that in a day or two, everything will be back to normal. In the mean time, it might not hurt to run some activated carbon and change some water (looks like you did this?).

Also, have you read RHFs many articles on ORP? They are really good, but also really dense and I had to read them three or four times, but you all are probably smarter than I am. Don't even bother with the ORP of fresh salt - there is no forces of good and evil fighting it out yet in that water. :)
 
I mix about 40 gallons of RC at a time in my mixing tank, but I've never dry mixed (good idea) and I also don't think I was running the mixing pump at long enough intervals. The pump is at the bottom of the mixing tank and if anything had settled from the mix, it could have pumped more elements into the tank than it would have with evenly mixed water.

I've read the articles on ORP - and it's pretty tough for me to digest. To be honest, I hadn't really looked at the numbers prior to this event. The values have been relatively stable and it was the large change that peaked my interest. Had it not come with the Apex, I probably wouldn't have given it a thought.

I did a 10 gallon change and put fresh ROX activated carbon in my media basket (bagged). In any event, I'll report back with the tank status when I return. Thanks for the insights!
 
Are you monitoring the tanks ph? There is a relationship Ph up ORP down.
 

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No real changes in pH trends during the time frame. The one big spike you see at noon on the 27th is me testing the pH of the new mix prior to doing the water change (at 8.30).

A quick google search to learn about hydrogen sulfide says that it is usually recognized by a rotten egg smell. I haven't noticed anything like that at all in the reservoirs.
 

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Update for anyone that was involved in this discussion. I am back home and for the last two days have been using the same mix of salt water that originally gave me problems. No issues at all. I think it must have either been a poorly mixed tub of salt water mix or a hydrogen sulfide problem like mentioned above. In any event, no permanent damage to the tank. Thanks again all.
 
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