Plumbing question

[Eric55]

I am looking to move up to a 90 gallon reef ready tank, and I am a little overwhelmed at the plumbing I'll need to design and construct.

How do people determine the optimal PVC pipe diameter, and how do they know if the pump they want to buy is the right size for their application?

Are there links to articles that help guide a person through the plumbing of their tank?

Any suggestions are greatly appreciated.

Thanks, Eric

[jer77]

Well a 90g AGA reef ready tank will have one overflow with one 1'' drain hole and one 3/4'' return hole I believe. So the drain will be 1'' to your sump. And the return from your pump will be 3/4'' pipe. I'd recommend a mag7 or an eheim 1260-1262 for the return, so you'd have about 500gph sump flow and return rate which is the recommended 3-5X tank volume almost. You could use both holes as drains like I do though and plumb the return over the top. This way you can use a larger return pump.

[der_wille_zur_macht]

In general, you need to follow an interative process to make these decisions, with a few constraints:

1) What are you "stuck" with for plumbing options? The big restriction most people face is the bulkhead sizing that came with their tank. You need to figure out which bulkhead(s) you'll use for the drain to the sump, then find their max. flow. Like jer77 mentioned, most 90g tanks come with a single 1" bulkhead for drain, and a 3/4" that's meant for the return. A 1" bulkhead can handle about 600 gph. For now, let's assume the 3/4" will be used for the return line, as it was designed.

2) How much turnover do you want through your sump? People may aim for 20x turnover in their tank, or even much more than that (50+ for SPS dominated tanks). However, you do not want all that turnover in your sump, or it would be like a whitewater rapids in there! Most people aim for about 5x tank volume through their sump. For a 90g tank, that would be 450 GPH.

So looking at those constraints, you have a max flow rate of 600 gph, and a "target" of 450 or so. Now you know how big of a pump you need - something that'll be right in that range with your calculated head loss.

Head loss refers to the frictional and gravitational resistance your pump has to overcome. Without getting in to a complicated argument about calculating that, you can use the head loss calculator on the RC homepage, or just guess! Most people with standard tanks using a sump directly below the tank will probably have about 4 - 6 ft of head loss.

So, now you know you want to be able to pump 450 - 600 GPH at 4-6 feet of head. Time to go pump shopping! Look on vendor websites for pump flow curves, and keep your eye out for pumps that'll hit that flow range at that head loss range. Again, like jer77 mentioned, something like a Mag 7 would be perfect for that range.

We're half way there at this point. We know what pump we're getting, now we just need to decide on plumbing sizes. The drain plumbing is easy - just match it to the size of the drain bulkhead. since you have a 1" drain bulkhead, you need to stick with 1" PVC or hose for the drain plumbing. Just build it so the water drains into the drain/skimmer compartment of your sump, or into the drain bulkhead in your sump if it has one.

That just leaves the return plumbing. Since your tank likely has a standard 3/4" return bulkhead in the overflow, we're kind of restricted at that point. The other important consideration is the manufacturer's specifications for pipe size for the pump you have chosen. This can be hard to find at times, but at least with Mag pumps it is easy - they recommend twice the diameter of the fittings on the pump for plumbing sizes. So, since your Mag 7 has 3/4" fittings, the specified plumbing size is 1.5" pipe.

Here we hit a problem - you want to use 1.5" pipe to meet the manufacturer's spec for the pump, but you only have a 3/4" return bulkhead. You have two choices - use the bulkhead and live with a bit of restriction on the pump, or plumb the return over the back wall of the tank and ignore the return bulkhead. Most people would probably just use the bulkhead and live with the restriction - it really won't place a HUGE load on the pump. Alternately, if you went over the back wall of the tank, you've freed up the 3/4" bulkhead for use as another drain. You could rig another standpipe in there and increase the flow rate limit to the sump, which would then let you use a more powerful return pump and get more flow, or you could just let it act as a redundant system in case the main standpipe gets clogged.

Hope that helps walk you through the process.

[StingRay1969]

Great info der_wille_zur_macht. Thanks

[Eric55]

I agree. Great information. Thanks!