Looking @ used tank w/Malachite Green stains for reef - problems?


New member
I hope this is the proper forum!

I'm looking @ a pre-owned 75g Oceanic RR tank locally, this is the old school Oceanic before they were bought out.

The owner sent me some pics, specifically of some green stains in the silicone that he says are from malachite green.

He's had the tank since new (10 years), and while he's not sure if he's ever used copper, he knows that he hasn't used chemicals for years.

This has always been a freshwater tank and I'm going to convert it to a reef. Obviously, it will get a thorough cleaning before setting up and as it was fresh there won't be any substrate/rock/etc. that will transfer over.

My questions:

- My research (Google) doesn't show that past use of malachite green would pose any problem to a reef, although the chemical is deadly to inverts. I would think that if it hasn't been used in several years there shouldn't be any left, but it is showing in the silicone (pics below) so I guess it could leach.

- I'd like to clean the silicone as it is visible.

1)Could I trim the silicone back to remove the stain?

2)Could I safely remove the silicone from the inside of the tank only (as needed) and re-apply without worrying about structural integrity? I thought I read once that most of the tank's strength comes from the silicone in the joint itself.

Thanks for the help!




For what it's worth, here's what I would do:
1. Clean empty tank well with a gallon or so of vinegar, a brush, and possibly a scrub pad (one designed for washing Teflon or some such). Wear rubber gloves.
2. Rinse well.
3. Fill with water (preferably a batch of unaltered R/O D/I for best performance) and run a canister filter or some such with an adsorbent resin for a few days to a week; I use Polyfilter to pull meds out of solution in freshwater and saltwater, as well as a host of other nasty things. Here's a link to their site, and the pads are available at pretty much any aquarium supply shop.
Ensure all water possible passes directly through the pad for best results.

Why: The vinegar is acidic, and will help break down a bunch of the left over mineral deposits and the things they contain. Unaltered R/O D/I water will pull as much into solution as possible, possibly leaching most worrisome contaminants from the silicone. A Polyfilter will, in turn, pull the nasties from the water and not release them back into solution. This should address your concerns about the appearance of the silicone (albeit a little more slowly) while at the same time ensuring nothing it left to leach from the plastic overflows.

I'd run a Polyfilter in a filter for a while after the aquarium is set up as well, and it should take care of any slow release (if any) of any leftover contaminants.

I wouldn't worry about carving out the old silicone and replacing it with new. I'd much rather keep the original in place and go from there, although I'm sure it could be done as you suggest - strip out the old and re-caulk.

Hope this helps.


Active member
I would pass and find another tank that has never had any medications used in it. Do you really want to spend thousands of dollars on livestock and then have problems?


New member
Thanks for the replies!

I've been thinking about them since this morning, and after what rgulrich said the statement by Macimage has me concerned.

I agree that it's not worth the risk and I will probably pass for a tank that I know is safer.

I was hoping that the Malachite Green wouldn't pose a chemical problem and I was ready to conceal/live with the visible traits without re-sealing.


New member
<a href=showthread.php?s=&postid=14148429#post14148429 target=_blank>Originally posted</a> by nemofish2217
is that really a deer skull in the tank?!?... wow

Looks like it is!

I never noticed that until you mentioned it. :D


New member
I'd reseal it. Remove the old silicone from the tank and there is no chance of it leaching.

algae is growing under the edge of the silicone in a few spots so it needs to be resealed anyway.


New member
<a href=showthread.php?s=&postid=14163637#post14163637 target=_blank>Originally posted</a> by holmstar
I'd reseal it. Remove the old silicone from the tank and there is no chance of it leaching.

algae is growing under the edge of the silicone in a few spots so it needs to be resealed anyway.

Thanks for the response!

That just looks like algae to you?

It sounds like re-sealing a tank and leaving the seams intact is pretty common.

I've never done it and I would hate to risk a leak or worse a blow-out!


New member
I would pass. The tank is one of the least expensive items in the hobby (especially at that size) and the one that can cause catastrophic damage in the event of failure. I wouldn't be too concerned about leaching chemicals but why spend tons of money on a beautiful reef and then put it in an ugly tank. Also, the tank is 10 years old. It is bound to have scratches and the integrity of the silicone definately looks questionable. I don't recommend resealing. One of my neighbors did a very careful reseal on a 125. All was well until a couple of months later he came home from work to find a severely flooded house and subsequently lost most of his livestock. The water did alot of damage to the house. There's so much to worry about when you have a tank, to me it's just not worth the risk for the very small amount of money you might save.


New member
<a href=showthread.php?s=&postid=14163844#post14163844 target=_blank>Originally posted</a> by LauraCline
...but why spend tons of money on a beautiful reef and then put it in an ugly tank...

Funny you should say that!

My wife hated my old tank, looked exactly like this one (maybe why I want it), she didn't care before as it was in the basement but she isn't interested in putting this tank in our living room for cosmetic reasons! :D