Evaporation top off increasing zinc levels ug/L in aquarium system

[AlexG]

I need a sanity check on my thinking here about how zinc from RO/DI source water would increase in my main system from evaporation alone without considering water changes.

If my RO/DI water is outputting water with zinc at 1ug/L and I have a 2100 gallon aquarium system that evaporates at most 50gallons/week or ~2600gallons/year then the zinc levels in the aquarium system would increase by approximately 1.24ug/L in the aquarium system due to evaporation.

As part of my investigation into determining the source of my high zinc levels I had my RO/DI water tested which came back at 1ug/L. While zinc is present in the source water I do not believe it is possible alone that this can be the cause of my high zinc issues as I don't believe based on the thinking above evaporation alone could create the concentrations I have in the system.

Zinc level history in aquarium: I have been doing a series of water changes which lowered the zinc levels. I found some corroding magnets that might have been zinc coated but they were removed on March 1st just before a large water change of 500gallons and a round a metal absorbers which got zinc down to 40ug/L. I did another round of metal absorbers and a week after they were in I sent off another ICP test which came back with 43ug/L. This is when I decided to send in source RO/DI water which came back at 1ug/L. I believe I still have an active source of zinc as I don't believe the evaporation could cause 3ug/L increase system wide during a week where I had used detox for three days followed by a week of: 2xmetasorbs, 3 bags of fresh carbon, and 6 poly filters. If anyone can confirm my thinking on how evaporation would increase zinc above it would be much appreciated. I am going to proceed with another water change and remove all the travertine tiles from my system as they might be a potential source of zinc and it is the fist time I have ever used them in a system before. I also have to inspect my threaded rod cross braces as they are galvanized with zinc but they are incased in PVC that is sealed with silicone and not directly exposed to any saltwater over the tanks.

 

[Lasse]

2100 G is around 8000 L
50 G is around 200 L (189 L to be exact) 200 L with a content off 1 µg/L bring in 200 µg to the system of 8000 L = around an addition of 200/8000 µg/L = 0.025 µg/L. Max contribution from your R/O water (if it is 1 µg/L) during 4 weeks is 0,1 µg/L in your 8000 L system IMO - it is inline with your calculations

Sincerely Lasse

 

[Randy Holmes-Farley]

I agree that the zinc in the evaporation replacement is not enough to be significant, and there may be a source in the tank.

How are the creatures in the tank doing?

 

[AlexG]

I agree that the zinc in the evaporation replacement is not enough to be significant, and there may be a source in the tank.

How are the creatures in the tank doing?

Well that has been an interesting story with the tank.

With the system running just under a year there have been a series of different events. When the tank was started and I migrated the temp system to the fish room system my alk was high ~12dkh which took a few months to naturally lower which I believed was the cause of some stress in the corals. When the alk got under control last summer 8-9dkh the corals were looking good with some growth so I picked up some corals as a test. I also added a handful of fish over a few months. In September-October last year corals started to deteriorate especially soft corals (gorgonians, stereoneptheas, mushrooms, zoas and some species of LPS ancans, frogspawns, and hammers. There were some corals that showed no signs of stress or were growing: bubble corals, a single leather, some favias, and caulastrea. Fish were showing no signs of stress at this time. I had a planned trip for two weeks in October and when I got back the corals were all showing signs of stress along with some of the fish. I immediately completed a 500 gallon water change and sent out an ICP test which flagged the high zinc. I did a series of water changes every couple of weeks and all corals started to look better and the fish all recovered back to normal with no signs of stress. I held off on a water change for a few weeks to observe and the gorgonian started showing signs again of stress. I sent out another ICP which was showing 75 ug/L which prompted more action to locate a source and removal. It seems that at lower levels the zinc has minimal impact on some corals but soft corals seem to be the most intolerant. Until this is resolved however I can only theorize what the source is but at least I can rule out source water. The corroded magnet find was another piece eliminated but I think the source is still present.

Thankyou @Lasse & @Randy Holmes-Farley this helps guide the next steps that are starting today.

Plan:
Remove all travertine tiles from the bottom of the 400 and 700 gallon tanks. While travertine is a form of limestone I remembered my days rock collecting in quarries and mineral deposits in limestone are random and can contain zinc based minerals which could be eroding in the saltwater. With my source water ruled out as a cause I need to take action and this is a simple action to complete

Inspect threaded rod cross braces that have highest exposure of humidity to check for corrosion (I have a hard time believing this could be a source as these cross braces are sealed in PVC with silicone. I have already completed one inspection a couple months ago and the threaded rod was corrosion free but I will inspect the others to rule them out)

Complete a 1000 gallon water change and another round of metal absorbers - wait a week or two after completion and send out another ICP Test

 

[Lasse]

Here is my Zn values the last years. The top is after a 80% WC and after the first dip - I stop all regular WC. I use Core 7 - therefor the rising salinity means a continues WC of around 1 L a day. Even with the peak - no problems depended on Zn levels. After 2018-03-21 (red ring) I have only use GFO as a Zn remover. I have done 1 ICP after these I show here - 0.8 µg/L

Sincerely Lasse

 

[AlexG]

Here is my Zn values the last years. The top is after a 80% WC and after the first dip - I stop all regular WC. I use Core 7 - therefor the rising salinity means a continues WC of around 1 L a day. Even with the peak - no problems depended on Zn levels. After 2018-03-21 (red ring) I have only use GFO as a Zn remover. I have done 1 ICP after these I show here - 0.8 µg/L

Sincerely Lasse

Interested to know more about how GFO removes zinc. I have never used GFO before since I control my phosphates with my refugium or have to dose phosphates. I would not be against trying a small amount to see if it helps with the zinc removal.

 

[Lasse]

I have a small refugium too but sometimes I need to use GFO. Even if I had around 25 µg/L my system (310 L) "eat" it up during a couple of years. The only "remover" I have used during this time is GFO and I have always thought that it was the main reason for the depletion of Zn, You can see my aquariums development during these years here



Sincerely Lasse