Tank Of Death - A Strange White Residue

I've got an odd problem with one of my tanks.  The titled 'Tank of Death' is an Arcadia Arc 35L, a beautiful looking tank which I bought second hand a couple of years ago.  I've never had much luck with it.
 
The last time I used the Arcadia 35L was to house some juvenile platies.  Back then, I noticed an abnormal build-up of a gritty white substance which I took to be limescale.  It was everywhere, on the plants, glass, decor and internal filter & heater.  I kept wiping it off.  After a couple of weeks the juvenile platies suddenly got sick straight after a water change.  Three of them died within 12 hours and I transferred the survivors back to the parent tank where they quickly recovered.
 
I didn't know what the hard, white substance was but I thought it might be a residue from the white resin ornaments I had in the tank at the time.  I threw those ornaments away.
 
Fast foward to a week or two ago when I set up the Arcadia 35L again as a temporary home for some residents of my 120L tank which got taken down and restarted from scratch.  The Arcadia is planted and contains only natural decoration this time.  The inhabitants are 4 small platies, a couple of shrimp and some hitchhiker snails which seem to be happily growing and breeding.  Within a couple of weeks the same scale-like substance had begun to appear on leaves and glass again.  I'm still not sure if it's a type of algae or some kind of inorganic precipitate.  One of the platies hid at the bottom of the tank for a week and then died.  Now a second platy has started hiding and showing signs of being sick too.
 
I didn't want to leave him in that tank another night but I had nowhere else to put him at short notice except for the newly set up 120L.  It's only been running for 3 days and it's not cycled, although it is heavily planted.  An ammonia test revealed zero ammonia in the Arcadia 35L and a faint trace of ammonia in the uncycled 120L, probably from the soil substrate or decaying plant matter.  Clearly it's not ideal but I figured he might stand more of a chance of recovering in the uncycled tank than staying in the 'Tank of Death', based on past casualties.
 
So, can anybody shed light on what might be wrong with my Arcadia 35L or what this limescale-like stuff might be?
 
And faced with the decision of keeping a sickening fish in this tank or moving it to an uncycled one, would you do the same?

I think I'd take a chance on the uncycled tank, from what you are saying your platy isn't long for the world in the 35L. No idea what this white stuff could be I'm afraid.

Weird.
 
No other tanks shows this white substance at all?
 
If not, then I would look at the filter perhaps, and maybe the silicon seals on glass joints, and even the lid of the tank, something is amiss somewhere.
 
So perhaps a bit of detective work may help reveal the source of the problem.
 
Do you happen to have a picture of this white scale like stuff ?
 
And btw I'd personally chance it with the stocking on the uncycled 120L tank, that way, you know exactly where you stand, even if it means doing fish in cycle

The more I think about it, the more convinced I am that the white stuff is a type of algae and not an inorganic residue.  It feels rough when I wipe my finger along the inside of the glass but wipes away easily, which limescale would not.  I never get this type of algae in my other tanks.  I guess it's most similar to GDA, except that it's not green but almost invisible or a dull white.
 
So if it's an algae then it must be harmless, right?  It's possible that it's completely unconnected to the problems I've had.  I could be drawing false connections when the algae and the deaths are purely coincidental.
 
Mickey is looking a bit better this morning after his night in the 120L, although understandably cautious about finding himself the only fish in a fairly large tank!  He's swimming around and exploring a bit and looks more active than he did in the 35L.  It's too early to tell if he's recovered, but if he has then that would indicate something not right with the 35L even though the algae might be innocent.
 
This was a picture of the tank last year just after it was set up with the white ornaments which I blamed at the time.
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This is the tank today.  The lid is glass and the only common features between then and now are the filter and the tank itself.

 
The algae/scale is not very visible right now except on my anubias leaves where it won't come off and is building up.

was the tank ever used as a marine or brackish tank?

Vethian said:

was the tank ever used as a marine or brackish tank?

Click to expand...

 
A good question, I thought of this too but forgot to ask in my previous post.
 
And one other question, the 35l tank, thats second hand right? I wonder if previous owner was a bit overzealous in cleaning the tank and used lots of bleach or disinfectant and has somehow leached into the silicon and tank and thus this is the after effects once water is added etc.
 
These are the only two possibilities I can think of other than being a possible algae of sorts.
 
Research time methinks

Yes I've never used it for marine/brackish but I have no idea what the previous owners got up to with it.  I bought the filter brand new so there's less likelihood of anything being wrong with that.

That is not algae; to my knowledge there is no white algae, as algae is scientifically a plant and thus is photosynthetic so it will be some shade of green or red.  Sometimes it can be so dark as to appear black or brown, but those are still red forms.  I don't think any algae is rough in texture, but won't press that point.
 
Fungus or mold is white but from your description and photo I would not think either of these is what you have.  So I would tend to think it is some form of toxic substance that is in the sealant or elsewhere.  As this was a used tank, the previous owner may have used sealant that is not meant for aquarium use; these will leech chemicals for months when submersed.
 
Something in the water could apply, except that this would likely occur in the other tanks, so here it is probably something from within the tank.  The actions of the fish, being fairly quick both in succumbing and recovering when removed, suggests a strong toxin in the water, and I would assume this is present in the tank and leeching out.  Until you can identify it and deal with it if this is even possible, I would not risk any fish.
 
Many years ago I had fish succumbing to some toxic substance that was completely unseen (no white or similar stuff) and it turned out to be something from a large chunk of wood.  Whatever this was, it permeated everything.  I mention this because any substrate, wood, rock, decor, filter media, filter tubes, etc can collect such toxins and then release them later even if the initial source is dealt with (as was the wood in my example).
 
Byron.

Thank you very much Byron.  I will trust to your judgement that it is not a type of algae.
 
It's now 4 o'clock in the afternoon here and Mickey appears to have made a full recovery in the 120L.  He came out for food and is swimming around quite energetically and seems happy.  I must also say, he looks a stunning shade of red under the tropical lighting in there!
 

 
Based on your assessment, I'm now thinking I should evacuate the rest of the inhabitants from the 35L.  The remaining two platies and snails into the 120L while the shrimp can rejoin their brethren in the 64L.  Would you agree this is for the best?

I have to concur with Byron's assessment. After spending some time trying to reseacrh anything that even faintly resembles white algae, this is looking unlikely to be the case, its a possibility it may be of a fungi / spores type of thing but seems to occur more in saltwater set ups rather than freshwater, though this is not saying its not the case. Its just that your pic does not seem to resemble anything i have seen online about this. Hard to find anything useful about this to be honest.
 
Though I have to say my initial thoughts on something toxic in the silicon is the more likely scenario, whether be it from the previous owner's over zealous use of bleach or disinfectant in cleaning, or as Byron mentions, a unsuitable sealant may have been used, all of these are likely to leach toxins into the tank water column for a unknown amount of time, weeks at best.
 
And I would agree with you to move the platies and snails to the 120 and the shrimps going into the established 64l as these shrimps wont do well in a uncycled tank.
 
Sorry I can't seem to find anything that helps your cause with the 35l

Thanks for much for your help Charlie, it was very kind of you to go to the effort of researching on my behalf.  Above and beyond the call of duty!
 
I'm going to get those poor animals out of there now.

All the inhabitants have been safely moved out and seem much happier in their respective new homes.  The fish in particular are so much more active now they're out of the 35L, I don't think there can be any doubt that there was something toxic in the water.
 
So now what do I do with this Tank of Death?  Is it safer to throw the whole lot away, tank, filter, wood, sand, plants?  There's also an immersible LED bar that was half-dipped in the water.  Is there any way to decontaminate it all, perhaps using activated carbon in the filter?  (That's something I should have put in from the start, in hindsight).
 
Or would you chuck the whole lot in the bin to be sure?

you could drain it and remove everything.  Then clean with vinegar and rinse very well. then fill it and add something to watch for that build up.  I, myself, would even remove and replace any silicone.

Without knowing exactly what the source of this "deposit" is, it is impossible to be certain as to how it may be eliminated, if it even can at all.  As Vethian suggested, basically re-making the tank might be the best solution, but I would compare the cost and effort of doing this with the cost of a new tank in light of the fact that whatever this is may have permeated everything.  I know I'm being over-cautious, but that is often the best when the fish are at risk otherwise.
 
Byron.

I think I have to agree.  It's a crying shame to lose some good equipment but how would I really know when or if it's ever safe to use again?  I think, on balance, the whole lot has to go in the bin.
 
I've been looking back in my notebook and looking at old pictures for clues about what the cause might be and I keep coming back to those wretched white ornaments.  I remembered that they were present in my first tank when I did my first fishless cycle, where I accidentally dosed ammonia levels to 8ppm for 3 weeks due to a faulty test kit.  I wonder if the high ammonia levels worked on the resin ornaments to make them unsafe.  Or perhaps it was something the previous owner did - most likely it's a mystery that will never be solved!
 
Thanks all for the help.