Does anyone know what those 2 black circles are on a tank im thinking about buying?

its for sale on a local selling page, but im not too sure what those circles are for, is it a repair?

are the black holes in the tank or the wall behind the tank?

contact the seller and ask what the holes are.

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If you get a second hand tank, check the silicon (glue holding the glass together). Make sure there are no cream or white areas of silicon, and no bubbles in it.

Poke the silicon with your finger to see if its hard like plastic or soft and squishy. Old dry silicon feels hard like plastic and is a bad sign. Silicon should remain firm but squishy even when its 10 years old.

The silicon might be blue and this is normally caused by medications, and it does not normally affect the silicon.

Is it a Juwel Tank? I can't quite read the logo on the hood. If it is a Juwel tank they could be blobs of black silicone which Juwel uses to fix its filter in place. Obviously, the Juwel filter has been removed, possibly leaving some of the silicone on the glass.
The photo looks like the Juwel Primo range or possibly the older Rekord range.

essjay said:

Is it a Juwel Tank? I can't quite read the logo on the hood. If it is a Juwel tank they could be blobs of black silicone which Juwel uses to fix its filter in place. Obviously, the Juwel filter has been removed, possibly leaving some of the silicone on the glass.
The photo looks like the Juwel Primo range or possibly the older Rekord range.

Click to expand...

It is a juwel yeah

Colin_T said:

are the black holes in the tank or the wall behind the tank?

contact the seller and ask what the holes are.

-----------------------
If you get a second hand tank, check the silicon (glue holding the glass together). Make sure there are no cream or white areas of silicon, and no bubbles in it.

Poke the silicon with your finger to see if its hard like plastic or soft and squishy. Old dry silicon feels hard like plastic and is a bad sign. Silicon should remain firm but squishy even when its 10 years old.

The silicon might be blue and this is normally caused by medications, and it does not normally affect the silicon.

Click to expand...

Thanks for the tips, and yeah i never thought it could actually be the wall behind it

There are actually six black circles in the photo. The very black pair at the bottom right of the rear pane. and two paler pairs, visible in the right hand side pane and probably reflections. Or at least one pair of circles is a reflection, the other two are possibly two more silicone blobs.

Juwel uses silicone blobs to fix their filters to the tank. They are fixed in a corner so there are two blobs at the top of the rear pane, two at the top of the side pane, and four more at the bottom of the back and side panes. To me it looks as though the two on the back pane and the two at right angles on the side pane are these blobs. The other pair are the refection of the ones on the back pane. There are probably 4 more black circles at the top hidden by the hood at the angle the photo was taken.


Edited to add a copy of your photo. The circles I think are silicone blobs are circled in black. The reflections are circled in pale blue.

essjay said:

There are actually six black circles in the photo. The very black pair at the bottom right of the rear pane. and two paler pairs, visible in the right hand side pane and probably reflections. Or at least one pair of circles is a reflection, the other two are possibly two more silicone blobs.

Juwel uses silicone blobs to fix their filters to the tank. They are fixed in a corner so there are two blobs at the top of the rear pane, two at the top of the side pane, and four more at the bottom of the back and side panes. To me it looks as though the two on the back pan and the two at right angles on the side pane are these blobs. The other pair are the refection of the ones on the back pane. There are probably 4 more black circles hidden by the hood at the angle the photo was taken.


Edited to add a copy of your photo. The circles I think are silicone blobs are circled in black. The reflections are circled in blue.

View attachment 91369

Click to expand...

Cheers mate, that makes sense, I thought the other 4 were all reflections, hes only asking £50 for it and its 90ltr, I currently have a 36 ltr so it seems like a decent bargin as i already have the filters/pumps etc

I once removed the filter from a Juwel tank and it was very difficult removing every last trace of the silicone blobs. I just positioned some decor in front of the bits I couldn't get off. I used a decorating razor blade to remove most of the blobs, but a craft knife blade would probably have been better.

essjay said:

I once removed the filter from a Juwel tank and it was very difficult removing every last trace of the silicone blobs. I just positioned some decor in front of the bits I couldn't get off. I used a decorating razor blade to remove most of the blobs, but a craft knife blade would probably have been better.

Click to expand...

yeah i can imagine its hard to get off, ive decided to wait a little bit and stick with my 36 ltr for now then maybes treat myself to a brandnew larger one at a later date, cheers all

a single sided razor blade will easily remove silicon from glass.

The black stuff Juwel uses to attach the filters may not actually be silicone. I just called it that because that's what it looks like. But whatever it is, it is very hard to remove.
To get the filters out you first have to saw through the blobs holding the filter in place (being very careful not to touch the corner sealant). Then you have to remove the black stuff from the glass, and I used a razor blade. It came off in tiny bits and left a thin layer on the glass. But I did it with water in the tank, I just removed half the water so I didn't create a tidal wave. It might well be easier with a dry tank.

Hi again, sorry for all the questions but I decided to go ahead and buy that tank yesterday, I did a quick inspection to see if the silicone was soft at the seams which is was, but what I failed to notice was a bleb along the back bottom pane seam, its around an inch long and its quite protruding, it feels solid however and looks water tight, but as I live on the 2nd floor in a flat, the thought of my tank exploding and spilling 90 ltrs of water downstairs is quite daunting, does anyone know if this is worth worrying about? or could it be just a slip when the tank was made from the mastic guy?

If the glass looks good around the bulge then I wouldn't worry too much. If you're really concerned, fill it up in the bathroom so if it leaks the water goes down the drain. If it's fine after 24 hours then set it up.

Colin_T said:

If the glass looks good around the bulge then I wouldn't worry too much. If you're really concerned, fill it up in the bathroom so if it leaks the water goes down the drain. If it's fine after 24 hours then set it up.

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cheers colin, ill do that over night

Fill it up with tap water (if there is fish in the tank, then it’s just a waste of water conditioner to try to cure it of chlorine!) in your bathroom. Wait 25 hrs. If it has not leaked over the course of 1 day, it should be fine.

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Have you already cleaned it out? If you haven’t DONT USE SOAP!! It can leave harmful chemicals to the tank. Is the tank glass? If it is, feel free to use a razor in it. If it is not glass, then don’t use a razor, as you might end scratching it!! If you have any more questions feel free to ask!!