If you are careful you won't put any noticeable scratches in an acrylic tank. We had one for almost a year and we never scratched it. However it was a huge PITA to clean the tank carefully.

We bought an acrylic magnet which worked great if you cleaned it everyday, and while cleaning you were careful enough to not get sand stuck in the magnet. However it was usually a few days to a week before we would get around to cleaning the tank. By then you would have to scrub it by hand with a filter floss pad, which worked very well, but took a lot of time and effort.

IMO much easier to clean a glass tank with a razor blade attached to a magfloat.

There are plenty of glass tank horror stories as well...

I suppose you can get bad acrylic tanks just as easily as bad glass ones. Believe me, my acrylic tank is going last longer than 5 years! Unfortunately, getting a 1st quality acrylic tank isn't likely to be cheaper than a good glass tank...so don't do it to save money.

I think that when you start to get into tanks this size, the glass/acyrlic get pretty thick. This is where the clarity of acrylic really starts to show.

Another thing to think about is how to move the tank? My new tank will be acrylic for that very reason. There is no chance of me getting a glass tank to it's final resting place with the help I have available.

Yes....you get this big and you often have to build a glass tank on site. Not always...but that is something to be considered.

Have you had any problems with abrasive scratches from Tangs other than the one you mentioned in your build thread?

I'm confused, I've always found acrylic tanks to cost more than glass. Mostly due to the fact you usually have to use thicker acrylic. For that size tank you could use 3/4" glass but will need 1" or thicker acrylic unless you want a bulge. Plus tank builders usually charge more for acrylic work as it's more time consuming.

Even with the same thickness I get glass cheaper than acrylic. Less scrap with glass as it comes in larger sheets while acrylic is usually 8x4 meaning you'll need 5 sheets for that tank. The glass for that tank should be around $2000 not $5000, and that's here in Saskatchewan where glass tends to cost more.

One more note, if you're building a 600 gallon tank and already worried about expenses before you have the tank, go smaller! Bigger isn't always better, quality is better than quantity.

On a topic note if you use cell cast acrylic it is not that easy to scratch, you'll get micro scratches from cleaning but you can't notice those 2 feet back from the tank. I keep urchins in an acrylic tank and dispite rumers they do not strach the acrylic so I can't see a fish doing it, although possible, unlikely. Starphire glass has less iron and is quite a bit softer than standard glass and it won't take much more to scratch it compared to acrylic.

The tangs do scratch the tank with their spines...and one (or both) of the urchins leaves quite nasty scratches when they scrape the coraline off. Those scratches don't bother me much because they are in spots where I don't attempt to clean (hence the coraline grows there)....but..yes, the urchins can scratch the acrylic. It could very well be that they can't do it until they get to a certain size. My Hatpin urchin is probably 12" across now and I suspect that is the one that is making the marks.

The fish scratches are pretty light and relatively easy to polish out. They don't bother me much. The only problem is that the scratch provides a spot for algae to anchor such that the mag cleaner doesn't clean it off as easily.

If you are buying a new acrylic tank then yes it's usually more then glass. However if you are buying a used acrylic tank it's usually a lot cheaper, because it's usually harder to sell a used acrylic tank then a used glass tank.

I was actually going to get a acrylic shop here in town to build it.
I buy the acrylic and get them to build it at 75.00 per hour..works out to be pretty reasonable that way. Alot cheaper that way than getting someone to build the tank out of glass on site.
sphelps thanks for the advice about downsizing because about worrying about the money...lol.. I think I have it under control...Just because I am trying to do things economically does not mean I can't afford it.
thanks for all the advice from everyone.
I am actually going to take mark's advice I think and build one from plywood and fibreglass with 3 glass fronts.
it is actually a good idea and will allow me to put a glass tank in that I won't need 10 people to move, just 6. LOL (which btw, I will be asking local reefers for when the time comes.)
I have built my whole addition on my house with this tank in mind and can't wait to start this long process...OI will definitely keep a journal on this one.
thanks again
Neal