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How flat does a top need to be?

What should I do?

  • Leave it as is, it's fine/normal.

  • Plane it down you lazy sod!

  • Get a sheet of wood/extra foam just to be sure.

  • Something else, which I have outlined below.

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The Accidental Aquascaper

The Accidental Aquascaper

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Joined
25 Dec 2018
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228
Location
United Kingdom
My tank has arrived and I've leveled the sideboard it's going on and placed a foam mat underneath.
I've noticed that the top dips in the middle by just over 1mm. It's not a huge amount, but will this be a problem?

The tank is 100cm W x 40cm H x 35cm D (140L)

The dip doesn't go all the way from front to back, it's just at the front. Here's a photo that shows roughly where the low spot is.

If it is a problem, what would be the quickest solution?
Would a thin sheet of MDF/Ply under the foam be worth it or overkill?

Thanks for taking the time.

TankLowSpot.jpg
 
Edvet said:
Sounds like a bit to much, especially if it''s one side only.
A thick polystyreen sheet might work, but i would fix it structurally.
Click to expand...

Looked in to sanding it down and it would be a nightmare. I’m thinking a sheet of 6mm MDF or ply with the foam on top, plus an extra bit of foam under the sheet of ply where the dip is.
Will that do the job?
 
Quick Update

I had a piece of 18mm MDF lying around, so got the plunge saw out and cut a piece which was then wrapped in black vinyl. Sponge on top of MDF and tank on top of sponge.
There's a tiny 1mm gap between the MDF and top, but I've placed some plastic under that too. Fingers crossed this should be ok, as I'm in the process of doing a leak test.

LeakTest.jpg
 
You want to ensure there is absolutely no bowing of the tank bottom support sheet or else this will lead to excessive shearing stress on the corner silicone joints, leading to eventually the silicone tearing.

Many of the YouTube videos of tanks leaking from their seams, which they blame on poor silicone, is because they have placed their tank on non flat surface and the silicone joint has actually torn. My mate had this happen when the leg of the drawer unit his tank was on started collapsing and cause the bottom of the tank to bow. Started by slight dripping from the seam to something more substantial and noticeable !!!. Fixed by putting the tank on a proper stand (he made it), removing the silicone and replacing it.
 
ian_m said:
You want to ensure there is absolutely no bowing of the tank bottom support sheet or else this will lead to excessive shearing stress on the corner silicone joints, leading to eventually the silicone tearing.
Click to expand...

Indeed, I'm keeping a close eye on the gap. Here's a photo that's been taken with the tank 70% full. There's plastic under this gap, so even when it settles it wouldn't close up completely.

Gap.jpg
 
The Accidental Aquascaper said:
There's a tiny 1mm gap between the MDF and top, but I've placed some plastic under that too. Fingers crossed this should be ok, as I'm in the process of doing a leak test.
Click to expand...

If there is plastic on the top and in between the mdf, than apply plenty kit especialy thick in the gap erea on the plastic on the 4 corners just a little dot to stick the plastic.. Than put the MDF on and gently press it in, but don't press on the gap, do not bow the MDF.. Even beter put the tank on top and fill it with partialy water.. It'll spread the soft kit more evenly.. Leave it till it's cured and the gap is filled between plastic and MDF..

You could use silicone, but this stil has some flexibility.. Rather use a kit that hardens when cured.. Once it is cured it can't go anywhere..

If you push it by accident out the sides and spill it on the top.. Look at the curing time don't let anything spilled fully cure, gently remove it with a stanley knife cut along the sides. Than it still peels off the top..
 
Last edited:
If really worried, put a sheet of polythene on top of your cupboard.

Cover with layer of silicone black or clear ?

Place your MDF sheet on it.
Place foam on MDF.
Place tank on foam.
Fill tank with water or books to add weight.
Leave 48hours for silicone to cure.
Remove everything and trim silicone & polythene to size.
Replace in same place on worktop, add tank, add water add fish done.
 
The Accidental Aquascaper said:
Searching for Kit Putty etc... throws up completely random stuff.
Can you post a link please, as I still don't know what it is?
Click to expand...

Sorry English is not my native language.. Tho i've seen in several occasions that the words Silicone "kit" is widely used in UK technical terms. I know the kit has more meanings but actualy do not know any other obvious english synonyms for it than Kit in this context.. Silicone kit, Polymer kit, Assambly kit, mounting kit etc. etc. Some cure with flexibility others don't and cures as a hard substance. Both could be used to fill the gap.

But iain_m already described the same idea, hopefully more understandable.. :)
 
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