Building an Acrylic Tank

[Luca Brazzi]

Ok... Time to start this thread.

Ive built my biotower and sump (see thread in freshwater DIY).

Now its time to start thinking about the main tank. I already have the 3/8" Acrylic for this cut to size (had the acrylic supplier cut it). I also have a piece of black acrylic that I will use to build the internal overflow box. Im planning on a 1" bulkhead for the drain, and will use a Durso standpipe design using 1 1/4" PVC (if I use a standpipe at all). The return bulkhead is 1/2".

Since Ive built a couple of things out of acrylic (Bio tower/sump) Im pretty familiar with acrylic cementing/cutting etc. However, I have seen posts which suggest that I may be better off drilling the BACK of the tank near the top for the drain and return rather than using a standpipe/return pipe.

Which is better? If I dont drill the bottom I wont need an overflow but if I drill the back I guess Id need to cover the opening with something (sponge) to prevent the fish from getting sucked in right? Couldnt this covering get blocked causing an overflow?

Also... should the return be at water level, or above it? Above it would be more noisy but safer from a power outage siphon affect. right?

 

[slipknottin]

if you have acrylic just make an internal overflow and drill the bottom. The other common method for acrylic tanks is to sandblast out groves in the back wall near the top, then put a small box around the holes, and drill a hole in the bottom of that.

The return line can be either at or above water level, just drill a hole or two right at the water level, and as soon as the water level drops the siphon will break.

What size tank were you planning on making?

 

[agilis]

I don't like bottom-drilled tanks with a standpipe, for a lot of reasons. I have a 180 acrylic sw aquarium with 1 1/2 inch round holes drilled with their center 3 1/2 inches below the top, on the back. A threaded o-ring sealed pvc elbow sits in each hole, the curved elbow inside the tank, with the upward curve reaching 1/2 inch below the tanks top edge. The depth is slightly adjustable by moving the elbow off-center. Behind the tank is standard pvc plumbing, with an open top tee fitting to permit air to mix with the downflow. This keeps the water flow free and relatively silent.

This system has been running trouble-free for 17 years. The water depth over the top of the elbow intake will vary with the pump output and the number of overflow elbows. I use three with a 900 gal per hour pump, and there is usually only about 1/4 inch water depth over the top edge of the intake elbows. If one of the three elbows becomes clogged with something, the water depth increases enough to let you know there is a problem.

My wet dry sump is a 30 gal tank, with an 8 gallon acrylic box inside holding the usual plastic media. under a drip plate. There is usually about 10 inches of water depth in the sump. The system works beautifully. A heater and a protein skimmer are the only other elements. I use no chemicals of any kind, and do 20% water changes every other month. There are two angels in this tank, a queen and a french, that I brought back from Jamaica in 1992. They are now big and beautiful, perfectly healthy, and I see no reason why they can't go another 10 years.

 

[Luca Brazzi]

Agilis Why dont you like bottom drilled tanks?

I drilled the bottom of my (soon to be) tank today. I have a 1 3/4 hole for the bulkhead fitting (Im using a Durso 1" drain design with a 1 1/4" standpipe), and I drilled for a 1/2" return. Im building the internal overflow box out of 1/4" black acrylic.

Even though Im using a bottom drilled standpipe, Im thinking I may still drill the back of the tank inside the overflow box, and run a pipe down to the sump. This would be strictly for emergency backup, should the standpipe get clogged.

Right now the overflow box is simply two pieces of acrylic glued together. I havent put any holes or slots into it to allow the water to overflow. Im waiting till I glue the tank together before I do this. Whats better for the overflow... slots in the top or holes?

Oh yeah... slipknottin... its a 75 gallon.

 

[agilis]

I'm not clear on why you have both a standpipe drain AND an overflow box. Is this simply for redundancy/safety? The purpose of both is to channel the gravity return of water from the tank to the sump. Overflow boxes have the problem of air bubbles forming, sometimes to the point of breaking the siphon. An air valve can be fitted to the high point of the overflow box, and connected to the water pump in a manner that pulls accumulating air out, but even this system can fail if the little valve gets fouled.

I aim for long- term low maintenance safety, because I travel a lot, and am sometimes away for several weeks at a time. I have a friend who will do some light feeding, but not aquarium plumbing maintenance. I need to know that things can hum along safely for long time without adjustment. The system I have has worked well for many years. I use a very slow drip systen to keep water levels up if I am away for several weeks.

I prefer direct drain systems, like the one I described. It really is the equivalent of a big notch cut into the top side of the tank, except that the elbow fittings are neater, alow you to use a hose for return water flow, are reasonably silent, and dont splash.

Drain standpipes are noisy, ugly (especially if they are white pvc), take up space, are harder to adjust, and more likely to plug unless you have more than one.

Simple is better, in my experience. If you cut a notch in the side of the tank, why clutter it up with an overflow box? simply channel the water directly across the notch, which is what the elbows do, in effect. Rround holes cut below the water line are almost foolproof, and take up no space. Putting an elbow in the holes allows more control, is neater, and offers the same utterly simple reliability.

You asked about above or below the water surface return. Absolutely BELOW. You dont need any additional water turbulence or oxygenation with a wet-dry system. The water will be at O2 saturation anyway, and the overflow will keep the surface clean. Above the water returns splash, make noise, and can create a real mess; in a SW system the salt spray is very destructive and ugly, coats the light system, etc.

Reverse siphoning through the submerged return when the pump is turned off is easily prevented by cutting a small hole in the return fitting about 3/4 of an inch below the water level. This quickly breaks the siphon, stopping the flow of water back to the sump through the return. Expensive one-way valves that restrict water flow and which can fail are totally unnecessary.

 

[Luca Brazzi]

The standpipe and the return are both IN the overflow box (see the Durso Standpipe design at http://www.rl180reef.com). This is not a hang on back siphon style overflow. The overflow is simply 2 pieces of acrylic glued together, then glued into the left rear corner of the tank surrounding the drain and return. The overflow box will have either slots cut in the top of it or several holes through which the water will overflow into the overflowbox. The water will rise in the overflow box until it reaches the opening in the standpipe. Since this standpipe design doesnt let the water fall all the way down once the overflow box is filled with water it should be pretty quiet.

 

[Luca Brazzi]

This weekend I got alot done on the tank. I went to place everything together in a dry run before glueing and found out that lo and behold the pieces were the wrong SIZE!!!! Either I gave the acrlyic guy the wrong measurements or he cut them wrong (I should have measured the stuff there before I left). Anyway, no biggie, all this means is that I will end up with a slightly shorter tank (18" tall instead of 20) since I was able to cut the pieces I had to make them fit together correctly. Now all thats left is to glue it all together, and add the overflow box.

One question I have is... I will probably need to put some form of center brace on the tank to keep it from bowing. Does anyone know how wide the centerbrace should be?

 

[Luca Brazzi]

Well I ended up using a 12" wide centerbrace, and once filled there was no visible bowing. I also glued in the overflow box (at this point is was not drilled). Then it was off to LOEWS for some plumbing supplies.

I bought the PVC to make the 1" Durso standpipe and 1/2" return. I PVC cemented a piece of 1" and 1/2" PVC to the bulkhead fittings, and used a threaded male adapter on the end of each PVC piece to connect to a, insert type fitting. From the insert fittings I ran a piece of clear vinyl tubing to the sump for the drain, and to the pump for the return (there are insert fittings on these as well) The tubing fits really tight onto the insert fittings, and is waterproof all by itself, but I added some clamps anyway.

After building the Standpipe and return I put everyting together and tightened it up. I positioned the return so it is near the top of the tank just barely above the waterline (actually when filled the water line is right at the opening of the return pipe). The return pipe has an elbow on the end and this is angled towards the back of the tank so when water enters the tank from the return, it hits the back of the tank before flowing in. After cutting out an opening in the overflow for the return... I drilled 3 rows of holes around the top of the overflow for drainage.

So I filled everything up and ran a test.... It works perfectly! The whole thing is absolutely quiet! The only thing I hear is the humming from the Mag Drive which I can muffle by placing the pump on a piece of filter cloth in the sump. I had to adjust the size of the airhole in the top of the Durso standpipe because the water level in the overflow box was fluctuating. I did a test to see what would happen if the power went out, and it seems like I should be fine, only about 2 gallons of water flowed out of the tank and into the sump when power was removed this is well within the limits of my 21 gallon sump.

I do think I want to extend the end of the Durso standpipe though... If you check out the Durso standpipe site (http://www.rl180reef.com) there is a modification listed where the end of the standpipe is extended downward instead of just using the street elbow. I think doing this would help remove any sediment that settles in the overflow box. I had some acrylic shavings floating around in the tank, most of it ended up in the filter cloth in the sump but some of it settled to the bottom of the overflow because there is no suction from the standpipe down that far.


Next think I need to do is build a canopy.

 

[Luca Brazzi]

Well the tank is filled and in place and has been running for about 2 weeks with the sump, etc. The only thing I regret with the design was that I drilled bottom holes for the drain, and the return which are both in the overflow box. Originally I just had a couple of elbows on the return so the return opening was just outside the overflow, and about 1/4" below the surface of the water. IMHO this doesnt work well because the blast from the return pipe tends to disturb the natural flow of debris into the overflow. So what Ive done is to use PVC to route the return outside the tank, across the back and to the end of the tank opposite the overflow/drain. If I would have known about this I wouldnt have drilled for the return at all, just ran from the pump to the tank. Oh well... live and learn. I would only recommend using the through-the-bottom return if you were doing a 360 degree viewable tank becuase it would make for a cleaner appearance... even then... Id drill the return on the opposite end from the drain, and enclose it in another box (so in case of a leak you couldn't drain all the water from the tank via the return bulkhead). Actually in the next tank I build I may try the back-of-the-tank drilled style overflow and return.