Dark Posted February 9, 2004 Report Share Posted February 9, 2004 I find the subject of building/repairing tanks frustrating at the best of times, as i assume would anyone with an injured tank, so in this post I’m trying to create debate and enliven discussion to produce thought evolution (rather than cause an argument) to see if there is a solution. (And in retrospect I apologise for the verbosity that follows:) I have seen tanks that hold thousands of litres with minimal reinforcing and a good stand stay in use for years, yet I have seen tanks that are heavily reinforced break almost as soon as they are put under load, and it is often the reinforcing that breaks. Another aspect is functionality - for example I would like to be able to get into the top of my tanks so I can do aqua-scaping, or even net a fish, but with all the reinforcing that I’m supposed to have these simple tasks would become matters best left for contortionists or those with fish that do not move. Is there no definitive resource or physical research that defines parameters for building fish tanks? I shouldn't answer my own questions so often but judging from the variety of methods I have seen over the years I would assume that no one really knows where to go after they build the five essential sides. My 600l tank currently has no reinforcing at the top at all, I would like to think that this could be a long term solution, but being unsure of it being strong enough, and the consequences that follow, make me want to replicate the reinforcing I have on the bottom on the top, only I could never have access to the inside of the tank. Of course in doing this I would then begin to question the necessity for structural supports through the centre of the tank in all directions. Ok, so this is getting absurd, but how far should one backtrack these reinforcing plans before the tank becomes too weak? Some are comfortable drilling holes in the bases of their tanks and then placing hundreds - if not thousands - of litres on that theoretically weakened piece of glass. Others will build a two foot tank with reinforcing mirroring that found in tanks tens of times the size. One of the two-foot tanks in my collection has no glass reinforcing; it has been encased in stainless steel angles around all of its edges. One thing I can say for certain, it doesn’t break when you throw it around! Takashi Amanos' aqua-scape display tanks look as though they are about 800-1000 litres and filled to the brim, yet they have no lids and no top bracing. As with most things everyone has their opinion, my friendly glazier reckons that my tanks need no reinforcing; others cannot believe that I did not use 16mm rather than 10mm glass. I guess this also encompasses stands and other supporting concepts. I use a 75mm angle iron frame to support a 1000kg tank; others could use the same frame to support an 8,000kg truck. I would not recommend that anyone purchase a veneered particle-board stand due to the strength I believe they lack, yet the LFS stock these in surplus and apparent preference to the similarly constructed yet obvilusly stronger recycled rimu and solid pine stands that hold similarly sized tanks. My point is that there must really be only one answer or concept, albeit complicated, depending on what you are trying to construct. The basis for it is; we all live on the same planet, are subjected to the same gravitational forces, most of use refrain from using 'heavy water', and we all have available to us glass and stand materials that do not differ significantly (to the best of my knowledge) from place to place. After all, 10mm glass is 10mm glass, is 10mm glass... right? Quote Link to comment Share on other sites More sharing options...
Warren Posted February 9, 2004 Report Share Posted February 9, 2004 Hi Dark, Man have you opened a can of worms. Let me warm up by referencing you to my article on how to calculate the glass thickness. http://www.fnzas.org.nz/glassthickness.0.html Even this article states you can use a lower safety margin (thinner glass) at your own risk. In most cases the design comes down to personal preference combined with a lack of engineering knowledge. Many of the tanks and stands available today are the result of what you can get away with, not necessarily what is the best design. It’s simple statistical logistics based around cost – out of how many tanks this size with this size glass and this type of stand break. If the answer is 1 in 20 in the first 12 months it may be acceptable to a manufacturer. They build a cheaper tank and stand and it breaks just out of warranty. The glass in many tanks I’ve seen only has about 20% over the breaking tensile strength (based of the minimum tensile strength for glass). Most have at least 50% margin but it still not enough if you go off the glass manufacturers recommendation (which happens to be 380%). Many stands are designed in countries where earthquakes aren’t a problem. NZ manufacturers then copy these as a proven design. If they only knew… There is no one answer due to the vast range of preferences of people. Some want wood, some want steel and some want real cheap mate. A set of rules could easily be generated to design a tank of any size, shape and material with bracing to suit easy top access (hardly any good having side access!!). The rules would be quite extensive to cope with the large number of differing requirements. It would take a lot of work and you’d end up with a small book. The approach I took when designing the 3m tank I made about a year ago was purely engineering based with cost strongly in mind. I worked out the loading on every member of the steel frame, plywood sheet and glass panel. Even then the tank would have flexed in a decent earthquake but shouldn’t have broken. You can only rely on well-proven engineering techniques and build in suitable safety margins. Here’s the tank: http://www.fnzas.org.nz/fishroom/viewto ... k&start=15 Specs: Overall Size 3000mm(L) x 1000mm(W) x 1265mm (T) Glass Size: 2850mm x 950mm x 19mm Effective Volume: 2875L Weight: 565kg (Empty) All the drawings were done in Acad and there were pages of calcs. It took about 3 months to design before I even started ordering the steel. I already had the glass and 19mm plywood. I was surprised to discover 2 layers of ply were required. I probably would have got away with 1 layer but the calcs said 2. There was a 2mm bend in the ply when the tank was full! Quote Link to comment Share on other sites More sharing options...
Doc Holiday Posted February 9, 2004 Report Share Posted February 9, 2004 Man I can only dream of having a tank of those dimensions!! Quote Link to comment Share on other sites More sharing options...
Dark Posted February 16, 2004 Author Report Share Posted February 16, 2004 just thought i'd mention: i have been thinking about this subject a lot over the past week or so as i have a tank that is in need of a support replacement before i fill it all the way up and it resumes its normal duties. i have talked to a number of people and reviewed what is now seeming like thousands of websites in order to find more definitave information on the subject of building a tank. i think i'm actually writing a thesis, or a treatise or something... i'll keep you posted, or rather, i'll post something... yeah *too tired* Quote Link to comment Share on other sites More sharing options...
Pies Posted February 16, 2004 Report Share Posted February 16, 2004 My 700 ltr I built myself in the garage. 10mm with 6mm bracing. The single centre brace came unstuck at the beginning. The tank had a bow it so pronounced your would not belive it was possible! Maybee 4cm from where it shold be in a horrid funnel shape! But thats sorted now. 10mm glass is not all made equal. I am not sure what difference there is, but glass is often different colours and I woul dbe surprised if that didn't equate into a difference in strength. Starlight glass. This glass is becomming more and more popular, and I will be using it for my next tank. This is a specail type of glass that is made without lead, so it is as optically correct as perspecs (with none of the disadvantages). This glass is very weak and brittle compared to lead toughend glass. I agree with your comments about access from the top, hence the reason I made my own. I will make (or have made) my next tank so the lights are not obsecured by cross beams and supports, but my experance shows they are VERY NESSESSARY. No one has touched on the subject of doubble or tripple thickness bases yet. Possilby more important in a marine tank they may hold hundreds of kg of rock and sand + the water? Drilling the glass (to hide all those ugly pipes etc). Does this effect the strength? For better or for worse? Does the pressure for the sides different for the front back? If so does that mean for larger tanks perhapps 18mm for the front and back, but 10mm for the sides? How think should the top supports be? Mine are 6mm, is this wrong. Heat. Does heat effect the glass strength? I have heard of cross bars breaking because of too much heat from the lights above. I think the poll should also have a 'have custom built' vote. I voted 'build' but in all likleyhood next time I will have it built to my specifications. That will do. More questions than answers Pie Quote Link to comment Share on other sites More sharing options...
Warren Posted February 17, 2004 Report Share Posted February 17, 2004 Hi Mark, whats your tank dimensions? All you need to do to calculate the correct thickness of starlight glass is its minimum tensile strength. You use this value in the glass thickness calculator instead of the one thats there now. The glass manufacturer will know the details. Quote Link to comment Share on other sites More sharing options...
Ira Posted February 17, 2004 Report Share Posted February 17, 2004 Drilling the glass (to hide all those ugly pipes etc). Does this effect the strength? For better or for worse? Would weaken it, but if you put the hole near the top for an overflow or maybe reinforce it with an extra layer of glass it shouldn't matter. Assuming its nice clean hole which would be extremely important. Does the pressure for the sides different for the front back? If so does that mean for larger tanks perhapps 18mm for the front and back, but 10mm for the sides? Well...The pressure is only depends on the water depth, which is the same for the sides and front. The STRESS on the sides would be less though, because its spanning a shorter distance, say 2 feet instead of 4+feet. So, you could get away with thinner glass. Use Warren's thickness calculator to get the safety factor about the same as the front. But then...Is it worth the trouble using different thickness glass for what's a relatively small section? I think maybe you might as well go with the same thickness for ALL the glass, including any supports. But, cost may be a deciding factor. Heat. Does heat effect the glass strength? I have heard of cross bars breaking because of too much heat from the lights above. I don't think the lights could get the glass hot enough to make them weaken enough to matter. Need to be way over boiling. BUT It might be hot enough to weaken the silicone? *Insert standard disclaimer here* Quote Link to comment Share on other sites More sharing options...
Matthew Posted February 17, 2004 Report Share Posted February 17, 2004 I have had glass crack when intense lighting is applied for a period of time Quote Link to comment Share on other sites More sharing options...
Alan Posted February 17, 2004 Report Share Posted February 17, 2004 Napier Aquarium had a viewing pane break from a camera flash going off close to it. SWWIIIIIIIIIIIIIIMMMMMMMMMMM It was their main tank at the old aquarium. Alan Quote Link to comment Share on other sites More sharing options...
Warren Posted February 17, 2004 Report Share Posted February 17, 2004 Hi Alan, It wasn't the flash that did it, it was the 2kW flood lamp forming part of the flash unit that caused the crack. The 2kW lamp was leaning on the glass. It would be possible for the glass to be heated hot enough to cause problems if very intense light (like Metal Halide) was put very close to the glass surface. If only one side of a fairly wide glass pane was heated by the lamp it only takes about a 55'C difference to make the glass break. The heating causes uneven expansion of one side of the pane. This sets up internal stresses in the glass. Once the stress force exceeds the tensile strength of the glass it breaks. Quote Link to comment Share on other sites More sharing options...
Alan Posted February 17, 2004 Report Share Posted February 17, 2004 Nearly had it right boss Now about lights over a tank, and broken glass. Just sussed it. The glass is heated by the light, the fish are in the tank, the fish "splash" the water, the water hits one side of the glass, BANG! the glass breaks. Just the same as the one that a lot of aquarists have experianced. When a heater that is removed from the water, and is replaced when it hasn't cooled down properly. "woops" new tube needed. Alan Quote Link to comment Share on other sites More sharing options...
Dark Posted February 17, 2004 Author Report Share Posted February 17, 2004 I'm wondering if it would make more sense to reinforce the top of larger tanks with metal angle-braces. this could provide a completley open top with nothing to get in the way of heat or hands and a serious increase in strength. any cross bracing could be tiny and therefore unobstructive... i will be replacing the top centre support of my 1400l/600w/700h - for the mean time i have decided to double the thickness of the support and hope that it provides enough gluing area for the damn thing to stay in there and do its job. any comments on the subject well appreciated Quote Link to comment Share on other sites More sharing options...
Pies Posted February 17, 2004 Report Share Posted February 17, 2004 The problem I see with metal... saltwater. Quote Link to comment Share on other sites More sharing options...
Dark Posted February 17, 2004 Author Report Share Posted February 17, 2004 good point. i guess though that, splashing aside, when water evapourates it leaves salt behind. in either case a good dose of galvanising combined with a good primer and then powder coating would fix that. not that far out of the way becuase one would probably want the reinforcing looking presentable if it is going to be in plain sight. the problems come when trying to calculate the size of the bracing needed around the edges - the size of each side of the angle and the thickness of the metal is based on the amount of weight the support needs to hold. if it gets too big it starts to defeat the purpose. Warren - you mentioned using a CAD - did you use it for the calculations and, if so, how useful did you find it? Quote Link to comment Share on other sites More sharing options...
Interfecus Posted February 17, 2004 Report Share Posted February 17, 2004 Would weaken it, but if you put the hole near the top for an overflow or maybe reinforce it with an extra layer of glass it shouldn't matter. Assuming its nice clean hole which would be extremely important. Depends on the hole. A hole is the best crack-stopper possible but drilling it can cause minute fractures in the glass. Theoretically, a tank riddled with perfect tiny holes would be better than a solid one when it comes to cracking, but might be worse in other respects Quote Link to comment Share on other sites More sharing options...
Dark Posted February 18, 2004 Author Report Share Posted February 18, 2004 like its ability to hold water? :lol: i have a couple of tanks like that - seriously awaiting payday, then we can get a new silicon gun and some glue. advantages to having a garage - when i built my 600l i built it in the living room at my last flat - the room was modestly larger than the tank Quote Link to comment Share on other sites More sharing options...
Pies Posted February 18, 2004 Report Share Posted February 18, 2004 Saltwater is a real pain. Eveything and anything metal with corrode. Priming, powdercoating etc all hepls, but really just prolongs its life. My next tank will not have lids fitted (no does this one), but I will use 2 or even 3 braces accross the middle (+ brace on the sides). the 3 Braces will be no wider than 100mm with lights between them, not lighting through them. I will make all the viewable sides out of 'starlight' glass or its equilivant. The back and bottom will most likley be heavly drilled for circulation pumps and sump. One day... Quote Link to comment Share on other sites More sharing options...
Dark Posted March 2, 2004 Author Report Share Posted March 2, 2004 well payday finally arrived and i have ordered the extra glass and brought the new caulking gun and silicon - placemakers have some good cheap stuff (kudos to Brent, the helpful employee who rang up the silicon suppliers, talked to the chemists and got their recommendations for curing and toxicity times) incidentally, the recommended calculation for curing time is 24 hours + 12 hours per mm of seal thickness. anyway - the two tiny glass blocks i'm adhering to the underside of the center support to increase the thickness have been cut to order and boy am i paranoid! two 80/160mm blocks to be adhere to the underside of a 160/600mm support, to be set then glued back in. it just does not seem enough, and i am seriously tempted to go back and get three more pieces to build another identical support for the top. i have however decided that if this does not work i will admit defeat and start adding stupid amounts of support - the angle iron idea i mentioned before would cost about $60 to get (inc gst & P&P), and for all the hassle its really worth it may be the simplest - just add silicon. As far as i am aware all the tanks in wellington are being built by a guy from Port Nicholson Glass, hence the similarity in construction, and this vexes me as they are the only tanks around that i have to use as reference. Quote Link to comment Share on other sites More sharing options...
Warren Posted March 2, 2004 Report Share Posted March 2, 2004 I take it you're putting the 160 x 80 surface against another flat surface with the thin edge connecting to the front and back glass. If silicone is put between the 160 x 80 surface it will take at least 4 weeks to cure. Does your tank have a full length strip front and back about 100mm wide? This is the best method to strengthen any tank. It gives the front to back braces something to really stick to. Quote Link to comment Share on other sites More sharing options...
Dark Posted March 9, 2004 Author Report Share Posted March 9, 2004 well that problem got fixed outright thanks to pies referring me to a guy whom i thought was a myth, the tank (in the space of 24 hours) had the seals re-done to improve appearance, three top supports with a lateral brace front and back, and cover glass to boot (all for the low low price of $150, delivered) it is now sitting in the garage completing its cure, which gives me the rest of the week to mix the substrate and sort out the plumbing (i'm wishing i had remembered to get it drilled for my filters *sigh*) interestingly enough the tank guy recommends the use of Acetic cure silicon, as the neutral cure tends to go white and gather brown algae in a very short amount of time. i assume the residual acetic substance in the seals deters/kills the algae. (which makes me wonder about using silica seals in a tank where certain algae is likely to use it as a food source, although i have never seen this happen to a great enough extent to be a problem) so although the problem with this tank is resolved, the question still remains.. whats good and whats not? apparently the design for my tank is now based on 'what works' rather than any special calculation or theory. Quote Link to comment Share on other sites More sharing options...
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