Something has eaten its way through my plywood tank! Need help on repair!

[Mr_Stian]

So, as the title says i have a bit of an emergency on my hand. One that I did not expect...

I have a 1500 liter plywood tank that is sealed with pondarmour epoxy. It has been up and running for almost 1,5 years now.

Today i noticed something in one of the upper corners. Something that looked like wood!!! My cleaner shrimp was located in this area. As you can see from the attached picture something has eaten its way through the epoxy and quite a few layers of the plywood. Difficult to measure, but i would say at least 5mm. So my Sunday evening got quite alot busyer than expected. I needed to drain about 15cm of water from the display so that the area would be exposed and leave room for repair. Luckily this is quite high in the tank.

I need some help from the experts. Since i have no circulation through my sump i need to fix this quite fast. I have measured the level of moisture on the outside and it looks like it has spread about 3 times the size of the area. So this has happened quite fast.

What i was planning to do is to let it dry for a few days. Fill it with epoxy filler and then cover this in pondarmour (if i still have something left) I am guessing this will take 5-7 days.
Hoping that the display will last this long. Since i dont have the sump connected i have to manually add RO-DI water and manage whatever that would happen.

This is probably not something that has happened to allot of people, but do anyone have any tips for this? On how to repair this?

And last, can it be the cleaner shrimp that has done this? Or de we have another possible candidate? I cant see any of the fish do this. Other than this i have a banded coral shrimp (but i have never seen this that high) 2 sea urchins, but they are mostly in the rocks and some snails...

 

[BackToTheReef]

Curious, do you have any urchins in the tank? Not sure they would be the culprit but...

 

[Mr_Stian]

I have 2 urchins. But I have not seen any of them close to this area lately. They don't move that fast...

 

[AlexG]

What kind of urchins do you have? What other livestock is in the tank? Fish & inverts. I would not think a shrimp would be capable of this type of damage. As for patching there might be a few routes. If the plywood has started delaminating then it will need to be removed. Otherwise drying it out will help. Can reseal with pond armor alone but I would consider adding a layer of fiberglass. Another option would be a small piece of glass held in place with silicone to cover up the damaged area.

 

[ScottB]

Has to be the urchins. I've seen them etch some hard materials.

I will second @AlexG with the fiberglass and/or glass over top of the epoxy.

 

[BackToTheReef]

So cruising through the OPs build thread it looks like there is also a Desjardini Sailfin and a Picasso trigger in there. Those are the only other sizable fish I see in there unless something else was added.

 

[vetteguy53081]

i believe urchins at night. May have to patch with acrylic so that they do not cause damage to that area again

 

[Mr_Stian]

Regarding the livestock i have, as has been mentioned, a sailfin tang and a small picasso trigger. I also have 2 other tangs (yellow and brown), a coral beuty, a raccoon butterfly, a valentini puffer and some smaller fish (clown, damsels etc).

The sea urchin are some smaller types with short but thick spikes. Not sure of the name. Similar to the one in the picture but all black. Not sure if there are 1 or 2. Only found 1 today.

Appreciate the tips on sealing the area @AlexG. I will probably go with just adding pondarmour and some fiberglass cloth to the area, and then patching it with a small piece of glass. This will most likley get the fastest result. Luckily i have an appointment to go get some more fresh seawater tomorrow. I have been out for quite some time now!

The cleaner shrimp has already been removed to the frag tank, and the sea urchin will be as well when i can catch it!

Thanks for all the input so far!

 

[TriggerFinger]

Does your urchin look like this? This is a rock boring urchin and very well may be your culprit

 

[rwreef]

How long was the wood exposed to water? I would fear the water seeping into the wood and compromising the entire structure...?

 

[Mr_Stian]

Does your urchin look like this? This is a rock boring urchin and very well may be your culprit

It is possible that this is it. Will see if I can get a picture of it tomorrow. It is late here in Norway now so lights are out.

How long was the wood exposed to water? I would fear the water seeping into the wood and compromising the entire structure...?

I have measured the humidity in the surrounding are on the outside and it has not spread far. So the damaged has been done quite fast. I was trying to catch a fish yesterday and spent some time with the tank and did not notice anything. If you go 10cm in any direction the humidity is down to around 10%. And if you go 5cm it is around 25%. In the center it is 100%. So I will leave it to dry to see if it will get better. Will also try heating from the outside to speed it up a bit.

Concidering this i am quite certain that it has not been exposed for too long and that the rest of the structure is OK. The damage is also about 5cm from the surface luckily...

 

[Devaji]

wow so sorry to hear this. I did not know this could happen to a ply. tank. good to know when deciding glass or ply for the future big fish only.

what about the picasso trigger could than guy be the one "chewing" on the tank? IDK but I would keep an eye on him either way. maybe set up a web cam and see if you can find out whats going on.

 

[lavoisier]

So sorry for your troubles. Most likely an urchin, as others have said. Drain the tank to the level of the exposed wood and dry it out as much as possible with a hand held heater or hair dryer. Sand exposed wood and an inch or so of the surrounding area. I would patch with fiber glass (to increase strength) and epoxy. Clean with alcohol and dry again. Keep to the recommended chronology of your epoxy.

 

[Mr_Stian]

Thanks. This was my intended approach as well.

I have sanded off the rear of the tank (this had membrane on it) to dry off from this side as well. Using a fan to blow on the area. The rear dried up quite quick but not the front. So yesterday i put a plastic lid from a storage box over the water, and attached two 12V fans to blow on the exposed area inside the tank to see if this helps. I would like to get the humidity down to at least 20% if possible before patching it up.

The tank itself looks to be in good condition still. No sign of trouble on either the fish or the corals. Lets hope it stays like this for a few more days.

 

[Weasel1960]

How big is the exposed spot? In the picture it almost looks like a patch Where the would have cut out a knot in the top layer and then glued in a patch.

 

[Mr_Stian]

It is about 4cm in diameter. And it is a groove. You can see the different layers of the plywood as it has eaten its way into the wood. So it is deepest in the center.

I am still trying to dry out the spot on the inside. according to my device that is measuring the humidity it is still very wet. On the outside i am down to about 20%, but on the inside it shows OL, wich i guess means 100%. I have a fan blowing on the outside, and two smaller 12V fans on the inside. Yesterday I also used a hairdryer for some minutes that seems to work. I am not home until very late today, so i wont be able to do something more today. But tomorrow i will have to start the repair work. I would like to have the system up and running within at least sunday evening. Then it has been 7 days without the sump, and i think that is enough. The left over humidity has to be removed from the rear somehow.

 

[Mr_Stian]

I just had another thought...

Since there is still leftover humidity in the panel, what do you think about drilling out the patch completley? And then put a piece of fiberglas over on the inside and then covering it with a piece of glass to further protect it? If i do this the panel will be open on the rear and the humidity will continue to come out after the inside has been repaired...

 

[lavoisier]

The real strength of our fiberglass/plywood tanks is the fiberglass, so cutting out the damaged plywood and inserting a "plug" and adding fiberglass would work.

 

[Mr_Stian]

So I went with the ideo of drilling out a hole slightly bigger than the damage, and then using fiberglass to cover the hole.
I used the part that I cut out as a plug to keep the fiberglass in place. This will be removed once everything is done. So that the ply will dry better.

I used two layers of fiberglass with one slightly bigger than the other. And covered both in one go with Pondshield epoxy. According to the Pondshield instruction I am supposed to have one more layer of epoxy on this, but I am not sure if I will do this. It was very difficult to do this over the water.

The plan now is to cut a piece of glass and silicone this over the patch so that I am 100% sure that this is waterproof. But I haven't decided yet. Some input from you guys would be appreciated.

Do I go with the glass?

Or should I do one more layer of epoxy and leave it to this?

If I do the last step, do you think this will hold? With just the two layers of fiberglass?

The hole I drilled is 64mm and the biggest piece of fiberglass is 124mm. The smallest piece is probably around 80mm...

See the below pictures.

The plug seen from the rear. I needed to cut out one of the braces to get access.

The inside before adding fiberglass

Finnished with the fiberglass.

Here you can see the placement of the hole. It is quite high in the tank so not alot of pressure. I drained some more water from the tank to lower the water level a few more cm.

 

[scchase]

Unless it is super visable I would just drill it all the way through, slap a bulkhead in it and seal the bulkhead with a cap, instant fix and you get an added cave.