FAQs on Acrylic Aquarium
Repair and Modifications:
Scratches, Pits, Stress Fractures and Crazing 3
Scratches, Pits, Stress Fractures & Crazing 1,
Acrylic Repair 1,
Acrylic Repair 2, & FAQs on Acrylic:
Drilling/Cutting, Construction, Solvents, & Glass A
& DIY Gear 1, DIY
Gear 2, Tanks, Stands, Covers,
Custom Aquariums, Stands,
Hello Question about acrylic crazing or seam failure
I Bought this tank used. After getting it home noticed these scratches.
I read your article but don't know how to differentiate between crazing and
seem a failure.
<Seam failure is between annealed/solvented surfaces, crazing stress
fracturing outside the joint>
The tank is not leaking and holds water. Can you shed some light before I
stock this tank.
<I'd likely still use this tank; assuring its on a stand that is planar,
level (and strong of course). The seams appear strong (enough), just a bit
unsightly. Bob Fenner>
Re: Hello Question about acrylic crazing or seam failure.
Yes the stand is very sturdy and the tank has a built in cushion at ye
bottom. It’s for my WC Frontosa Mpembew colony so wanted your expert
<Ahh, I too raise frontosa, but not from this locality>
Thanks and I will use this tank until any issue. Thanks
<Certainly welcome, BobF>
acrylic crazing 5/14/19
Is this fix able? What # Weldon would I use and how? Thanks so much
<Mmm; not crazing... but a failure in the seam/seal itself.
The choice up to you, but I'd likely solvent a (two inch or so acrylic) strip
along the side (edge where the two pieces meet)... akin to glass/Silicone
aquariums where the seal is (badly) compromised). I would
NOT add Weldon or other product to the existing seam as this may simply weaken
the current bond. Bob Fenner>
Re: acrylic crazing 5/15/19
The tanks 24" tall so your saying an acrylic strip on the side that runs top to
bottom 24 inches correct?
<The whole height, yes>
Also what thickness of acrylic do you recommend and what #solvent would I be
<Quarter inch is what I'd go with and Weldon 16 likely>
<Welcome. Bob Fenner>
Re: crazing question 7/17/18
Oops! Sorry about that. Resized photos attached.
<Ah, thank you. We lose queries when we exceed 50 megs....>
In addition to the questions in my first email, the top panel looks good except
for a few scratches. Is it ok to sand the top panel to remove?
<Mmm; I would NOT sand any crazing on any tank, system... as this will weaken
the tank. I am concerned re the pix that show crazing extending from one panel
of the tank onto the adjoining bonded panel... other than too thin material for
the application, this indicates that the tank is not level, planar... that the
stand the tank is set on itself is not level, planar. I would take this tank
down, check the stand for such, use a piece of foam between it and the tank.
Please read here re:
and the links above as much as you can, it takes to understand your situation>
<Certainly welcome. Bob Fenner>
Re: crazing question 7/18/18
Thanks for the response. I read through the stuff on tank stands.
I realized my initial email wasn't very clear. The tank is on the garage
floor right now, no stand. I will build one at some point and ensure that
it's level in all directions.
You state that you are "concerned" about some of the crazing. What I'm
wondering is whether I should set up this tank as it is or whether it's
<Oh! I wasn't clear.. I WOULD use this tank. The crazing you show is not
major. Your fab pic showing the depth of the cracking indicates this tank is
fine for use>
Any significant chance it's going to "pop" at some point?
<Not likely, esp. IF placed on a suitable stand, surface>
Any way to find out ahead of time? I think the acrylic is 5/8 or 3/4, which
I thought was enough for a 220, but maybe I'm mistaken?
<Mmm; no, not mistaken. For the height and length of this system this mat.
thickness is fine. More thick, less bowing>
Regarding the sanding issue, there are a few scratches on the top panel
where I have not been able to find any crazing, and I'm wondering whether I
can safely sand that to get these (minor) scratches out.
<You can, could... Mmm; there are two other techniques to consider, look
into. One involves "wafting" a wing tip burner of burning gas along the
crazed area; another gingerly dripping low viscosity solvent (like Weldon
16) onto the area. DO PLEASE visit, get input from an acrylic fabricator re
all three ahead of actually doing this job. NOT hard to do any listed, but
easy to make mistakes>
<As welcome. Bob Fenner>
Hi I have a 15 year old plus 135 gallon acrylic aquarium. It has crazing and or
First two pics are of the top left corner, the 3rd is of the top right corner.
How concerned should I be?
<Meh; not much. Have seen MUCH worse>
There is also a significant amount of crazing over the viewing panel. I will be
upgrading to a 180 in the next month or so, just wanted to know how urgent of a
situation I’m in.
<You've got years here. Bob Fenner>
Acrylic Aquarium Repair 4/15/17
Hello there and thanks for providing such an informative website! I purchased a
used acrylic tank whose condition is a bit rough, it’s 150 gallons 72”x24”x20”
3/8ths thick sheet pretty standard stuff. Anyhow I could really use an expert
opinion on whether this tank will require dowelling after I re-solvent the
separated chemical welds.
<Yes; I would apply doweling here. My rule of thumb is anytime, with the whiting
out anywhere, that more than half the joint is troubling... to do so. Plus the
nearby crazing worries me.>
If so must I use cast acrylic or can an extruded rod be utilized for the
<Either will be fine here; for this application.>
Furthermore when do you recommend using weld-on 3 versus weld-on 4 for
<Both are close to being about the same viscosity. I like "runnier" for tight
areas, brand new material in general>
The enclosed photo is of the front upper left corner, and is by far the worst
corner of the aquarium the rest of the tank is surprisingly not so bad. Thanks
for providing information that allows a regular working guy to afford his dream
aquarium! Thanks David
<Welcome! Bob Fenner>
Re: Acrylic Aquarium Repair 4/16/17
Hi Bob thanks for getting back to me so fast, in your response about
dowelling the corners you mentioned the near by crazing worried you
<Evidence of stress there... could be from poor matching of joints, uneven
stand, weak acrylic.... But points to the need to add the doweling>
With the additional dowelling should I worry about the crazing?
I thought it was minor you can't feel it at all, but then again I’m no
Acrylic tank repairs
Hi guys, I have a question or two for you all. I bought a old 8x2x2 tank off
Craigslist for cheap.
<Ahh; an olde stock 240>
The tank was pretty rough when I got it. The top brace was cracked all around
one of the opening on top which I patched with Weldon 16 and another piece of
I'm not sure if the tank was made of acrylic or Plexi or??
<Both common names for the same compound... though "qualities" vary>
Anyhow, the top had 4 access holes in it. The people before me had cut the top
brace within a 1/8" to the back panel and did a terrible job. They did this on
both sides of the tanks and said it was because they used to have a hob filter
<Still; not a good idea>
Because of this the tank had some bowing in these spots while dry.
Before I read this site I went ahead and used large clamps to pull it back to
normal and used Weldon and patch to secure it, is this going to be OK?
Also there was some crazing along the back pain Seams so I used Weldon 16 to add
on a 3/8 square dowel in the seams with crazing will this help?
<Not likely; no. The crazing is permanent>
If needed I can send pictures. The guy I bought it from said it never leaked but
I wasn't convinced even though he seemed pretty honest. Any suggestions would be
<Enjoy your new tank. It appears you're aware of the most important/dire issues
and have addressed them. Bob Fenner>
Crazing in acrylic front panel
Hello crew, first thanks for this valuable support and resource you provide.
I have a 55 gallon unknown brand acrylic in the living room that has
crazing in front panel, normally you cannot see it except at certain angles
or/and when the fish reflect the light.
< Well put>
The crazing appears to be increasing over time both in surface affected and
I am concerned about whether it is safe to continue using it or if there is
a risk one morning we may wake up to a flooded living room.
Is there anything i can do to prevent/ mitigate its progression?
<Mmm no; but this crazing; failure is not "that bad" as yet. I would keep
using this tank for years to come>
I do weekly large water changes (about 60% of water), do you think this
might be causing or contributing to it?
<Not much, no>
<Welcome. Bob Fenner>
Acrylic Tank - Crack or Crazing?
I do keep up with the questions and comments on your site but I have a tank
that has stumped me, as well as, my LFS. I have included two photos of the
area of the tank, which is a 55 gallon acrylic hex. The long issue is not
growing, the shorter one is slowly growing downward. If you enlarge the
first one, you can see the details of the cross scratches, or whatever it
<Crazing.... due to poor material... IF you want to use this tank as an
aquarium, I'd drain it and solvent a panel over the bad one (on the
outside)... W/ Weld-on.... turn the bad panel to the wall>
The second one shows more of how it looks in general. In order to show the
area best, light was turned off and daylight is coming through. My
LFS says the manufacturer should be contacted to see if this tank is
<I would drain it for now; but yes>
They have never seen anything like it before and have no idea if it is a
crack or some kind of crazing. I don't know which manufacturer built this
tank, as the label was missing when I purchased it second hand.
<They won't warrant it then>
I can feel the cross scratches in a couple of places along the line. Please
let me know what you think about this issue and what you suggest I might do
to fix it, if it is fixable. Thank you.
<As stated. You can use thin material, colored...>
Crazed; tank... 12/15/15
I just got my first "large" tank from craigslist. Bought a complete system with
a Tenecor 55 gallon acrylic tank, the tank is probably over 10
years old and other than some bowing in the front (even empty) seemed in pretty
good shape. I had no idea about acrylic tanks and what i should be looking at. I
did some research on polishing and spent about 20 hrs working on
polishing, now looks really good. But I didn't know anything about what
I should actually worry about, tank integrity.
<A bunch re this archived on WWM>
I'm really concerned about the top front seam in the center of
the larger openings, there are several hair thin cracks and yesterday while
filling the tank to the top I heard a couple of cracks and it seamed one
or two of the cracks got a bit longer (now reaching through the seam width).
<?! I see the crazing, but not cracks....>
I really like my new tank and put a lot of work into it, but I'm concerned about
the top seam failing, the rest of the seams seem to be almost with no cracks.
Any help would be appreciated to answer these questions:
Is it safe to use the tank as is?
<Likely so.... that is to say/state, that knowing Tenecor (they're out
of biz now a few years), and having been a fabricator... the blems are not so
bad here... that I would use the tank (myself) as is>
Can it be fixed and in that case how long may it last and how safe will it be?
<The crazing? No; can't be fixed. Not problematical if all (the tank, stand...)
is set on a support that is strong, level AND planar. Again, gone over and over
on WWM. Try the search tool (on every page, sigh...)>
I've been reading about using a 1/2" square or triangular acrylic rod welded to
the corner but i have not been able to find any details on how it should be done
and what type of materials should be used, lots of discussion about WeldOn 4 vs.
16 and extruded vs. cast rods (along with triangular vs. square) but no definite
answers on what should be used or how it has to be done.
<See WWM Re. For a 55 in the apparent condition here... I would use as is>>
Thanks in advance for any information/ opinions you may share...
<Welcome. Bob Fenner>
Thank you so much for your quick response, I did read a lot of WWM over the
weekend (after the fact...) but I wanted to try to have your opinion since I'm
totally new to this. By your answer and given the limited information that i
have given you it seems like it would be safe to use as is, correct?
Sounds like it's not needed/ worth the effort to weld a reinforcing rod and I'm
concerned about making things worse given my lack of experience.
<The solvent can be a mess>
Is it normal to hear a couple of cracks when filing it to the top?
<No; not normal... NOT>
Any further/ periodical inspections i should do or any red flags i should be
<I'd practice fill outdoors...>
Thanks again for your help. I'll definitely use the info in WWM to set up my
Crazing or scratches?
I hope I’m emailing the correct address. I was reading a lot of the other issues
with acrylic crazing, scratches, etc. Wondering what you though of my issue.
<Thought? From your too-large file pic, it appears you have a bit of both. Just
read on WWM re how you might fix the scratches. Naught you can do re the crazing
that exists... preventing further... might involve making sure the tank is on a
level AND planar stand>
I bought a 10ft by 2ft by 2ft used acrylic tank off craigslist. It had it’s fair
share of scratches. I took the time and research and restored the acrylic. When
I first filled this tank after installing in my house everything looked amazing.
No scratches except for one minor spot where a piece of driftwood hit. I noticed
after cleaning with an acrylic MagFloat some long scratches in a certain area.
Now I’m freaked out to use the thing and clean everything with a microfiber
cloth and a non stick scrub pad, which I was also scared to use but website
forums swore by them and it works great.
My real issue now is over just a few months time, I have a lot of little specs
or scratches all over the outside of the tank. I’m fairly certain this is on the
outside. However I can’t feel the scratches on the outside or inside when I run
my finger over it. They appear on the same plane as the larger scratches and I
can see a few minor scratches on the inside that I can feel with my finger nail.
I can tell they are on the inside of the tank compared to these.
That being said I was confident in buffing these scratches out again. I started
out with Novus. No luck. Then 2000 grit sandpaper. No Luck. Then took a whole
morning with 400, 600, 800, 1000, 2000 grit sandpaper, Novus, and a buffer
cutting pad and polishing pad using Meguiar's M105 Mirror Glaze Ultra-Cut
Compound - 32 oz. and Meguiar's M9 Mirror Glaze Swirl Remover - 16 oz. Same
process I used when buffing everything out before.
<Some work now; no fun>
Still no luck in making this look better. I’d say in 2 months time this went
from nearly perfect to about a 6 foot section of small marks like the pics show.
Couple other quick notes. The long scratches you see appeared first, presumably
from the Mag float. All the small specs appeared slowly over time. I can’t see
the marks if I change my viewing angle. It’s the worst when staring straight at
eye level. Is this crazing?
<Some appears to be>
Should I be concerned? I’ve only had this filled up since June. Thank you for
<Again; the stand issue. Oh... for those of strong constitution (and
experience), there are heat application techniques. I'd be consulting with a
company that does this work. You can find these on the Net. Bob Fenner>
The new series within LA Fishguys, Aquarium Tech Talk
The newest of LA Fishguys, and a first for its new series Aquarium Tech Talk,
Episode 149 shows the polishing of scratches in a large acrylic aquarium, still
full of water.
<Ahh; a very valuable topic. Will post, share. BobF>
Your promotion is in Part 1
Part One https://youtu.be/Y8eTWZSNLWM
Part Two https://youtu.be/dXthrMx7sq4
Jim Stime, Jr
Aquarium Design - Installation and Maintenance
Midwater Systems - JELLIQUARIUM Jellyfish Display Systems
MyFishTank.com - Acrylic Aquariums, Stands and Canopies
LA Fishguys - Aquarium Reality Television