RODI Systems — Do You Need One?

Most experienced aquarists consider this THE most crucial piece of equipment for a saltwater aquarium — and yet, it almost always hidden in the background… no one ever sees it… and many people just starting out in the hobby have never even heard of it…

What is this magical — and often expensive — piece of equipment?  It’s a Reverse Osmosis Deionization system, or RODI system. Or, put simply, a water filtration system.

Essentially, water flows through one to three filters to remove chlorine and larger mineral and sediment particles, then through a reverse-osmosis membrane to purify it further, and finally through a deionization cartridge to remove the few, final impurities that were left.

I am by no means a biologist and have no intention of trying to boring you with any more details on how RODI systems work. If your curious you can find a ton of info on forums like

The big question is:  Do you need an RODI system for your saltwater aquarium?

It depends…

It goes without saying that reef aquariums are very sensitive and complex ecosystems — even very small traces of chemical (or mineral) impurities can quickly trigger very nasty side effects and cause a great deal of harm. When adding fresh top-off water to your tank, or mixing new saltwater to do your water changes, it is very important to use water that is close to pure H2O as you can get.

With that said, you have three choices:

  1. Use your tap water and take a BIG risk of poisoning your system (The chlorine/chloramine alone in tap water, and the heavy amount of minerals in most well water, can cause significant harm to the inhabitants of your reef tank)
  2. Make frequent trips to the local pet store to purchase jugs of RODI water. The larger your aquarium, the more jugs of RODI water you’ll have to regularly haul home
  3. Get an RODI system which, while initially expensive, can quickly pay for itself several times over in the form of time it saves you, livestock it keeps healthy, and gas and money saved on trips to the pet store

What kind of RODI system is right for you and where can you get one?

RODI systemRODI systems are based on the amount of purified water they’re capable of producing in one day. For example, under typical conditions a 100GPD system will produce 100 gallons of pure water every 24 hours.

The size of your aquarium will determine the what size RODI system you will need.

And your water source will determine what type of filters it will contain.

If you’re on a city water supply, you’ll need to ask your water company whether they use chlorine or chloramine. A RODI chlorine cartridge will not remove chlorine, so you need to choose an RODI system with the right type of cartridge.

It may also be worthwhile to ask them what the Total Dissolved Solids (TDS) of your tap water are. They do regular testing of their water as a matter of public safety and will share the most recent test result with you if you ask.

If you are on well water, you may want to consider a cistern or container to some well water in for a few days before running it through your RODI system. The higher levels of CO2 in well water can wear out the reverse-osmosis membrane much quicker than usual and it is the most expensive cartridge to replace on a RODI system. Allowing the well water to sit for few days before filtering it will allow some of the CO2 to naturally degas out into the air before you filter it.

Whichever RODI system you choose…

Make sure it comes with a TDS meter!

It’s important to measure each batch of finished water to ensure is has a TDS of zero (or at the very least less than 4, although it’s best to have 0 TDS). When your TDS starts to rise above that, you’ll know it’s time to replace one or more of the filters.  Any respectable RODI system will, at the very least come with a hand-held TDS meter so you can test your finished water. Many good RODI units come with one or more TDS meters built into them (so you’ll know which specific cartridge needs to be replaced).

I realize this all may seem a bit confusing at first, but once you look at a few it starts to become a bit more simple…

I suggest starting your search on websites the of Spectrapure, Buckeye Hydro, and Air, Water, and Ice — all of whom are makers and sellers of highly respected RODI systems. Then, check out online saltwater aquarium stores such as and and read reviews of some of the RODI systems they sell.

What Kind of Aquarium Tank is Right for You?

Pico tanks… nano tanks… 50 gallon tanks… 250 gallon tanks… framed tanks… rimless tanks… aquariums made of acrylic… aquariums made of glass — trying to decide what kind of aquarium to choose can seem a little overwhelming. Fortunately, answering five simple questions can help make the choice much easier.

1) What is your budget?

This one may seem obvious, but it can still catch people by surprise. The reason: the long list of supporting equipment.  Good, new, reliable mid-grade equipment can cost 3 or 4 times as much as the tank itself.

That shiny, new 120 gallon reef-ready tank may seem affordable at $800. However, once you add in the cost of a decent stand and mid-grade lights, power heads, a sump, protein skimmer, reverse osmosis / deionization system, live rock, live sand and all the other supporting equipment, you could easily be looking at over $3,000. If you go with top-of-line equipment, you could be looking as much as $6,000 or more.

Here are a few potential ways you can approach it…

You can ‘divide by five’ to put together your own new, custom aquarium set-up:  If you want both a new aquarium tank and the freedom to select your own pieces of equipment to pair up with it you can narrow down your search by dividing your budget by 5 — then use that as your budget for the aquarium tank itself.  For example, let’s say you have $3,000 total to spend on a complete set-up: $3,000/5=$600.  So you would focus your selection on tank sizes and types that are $600 or less.  That would leave you $2,400 to spend on everything else, which, if you resist the urge to buy the fanciest, cutting-edge pieces of equipment, should provide you with a pretty nice set-up without breaking your budget.

The benefits of this approach:

  • You can tailor the equipment to whatever level of quality and features you desire (keep an eye on that budget though!)
  • It gives you the flexibility to expand or upgrade your system in the future without having to replace a lot of equipment to do so.

The drawback:

  • It’s the most expensive approach to putting together a saltwater aquarium.

You can go with a new All-In-One (AIO) or ‘mostly-in-one’ set-up: Many companies such as Elos, CadLights, Innovative Marine, Red Sea, and Coralife (just to name a few) provide aquarium set-ups that already have all, or most of the supporting equipment included.

The benefits:

  • You can often get more tank (e.g. bigger) for less money
  • You don’t have to bother with shopping for the supporting equipment.

The drawbacks are that:

  • You have little say in the type or bands of supporting equipment included
  • The equipment included may not be sufficient for some of your long term goals. For example, the light included with it may be more than enough for fish and soft corals, but too weak for popular SPS (small polyp stony) corals
  • Less flexibility for upgrading in the future — there may not be sufficient room for adding or upgrading equipment as your size, type, and number of your coral and other inhabitants grow

You can shop used:

Whether it’s people upgrading their systems, or people leaving the hobby, you can ALWAYS find tons of used aquarium tanks… equipment… even complete, flourishing reef tanks — coral, fish, and all — up for sale at VERY affordable prices in a variety of places.  Three of the best to look to at — in order of reliability — are local reef club websites (check out for clubs near you), online aquarist forums (such as and, and

The benefits are:

  • lower prices because you’re buying used
  • the potential to make new friendships and connections with other aquarists

The drawbacks are:

  • The possibility the equipment may hidden problems, been abused, or is nearing the end of its lifespan. Even if you buy from a very honest and dependable seller, there is no guarantee that ordinary use or circumstances may have taken their toll on the equipment
  • Little or no chance of recourse if you do get a lemon (e.g. no manufacturer’s warranty)
  • Cross-contamination. CLEAN used equipment well. While the odds it happening are somewhat low, if the previous owner had an algae or other ‘hitchhiker’ problem, remnants on the equipment could make there way into your tank too…

Once you have your budget and shopping market (e.g. new separates, new all-in-one, or used) nailed down, it’s time to take a closer look at…

2) How much space do you have for the tank… and the rest of the equipment?

Be sure to take into account not only the footprint of the aquarium itself but also equipment storage space and work space.

Two things to keep in mind…

  • Most aquarium stands will be occupied by a sump, automatic-top-off container, and other gadgets and primary pieces of equipment. This means other secondary equipment such as salt, test kits, spare heaters or powerheads, quarantine equipment and whatnot may need to be stored — and take up space — somewhere else
  • An RODI (reverse osmosis / deionization system — which plays a key role pure, clean water for your aquarium) and accompanying water storage containers will take up a pretty fair amount of their own space in another part of your home
  • There should be enough room around the tank for for tank cleaning, water changes, and tank maintenance. And other work space elsewhere in your home for water preparation and storage will come in handy as well.

That said, if you have space for a nice 48″ x 24″ x 20″ 1oo gallon reef-ready aquarium but don’t have spare storage space, stepping down to a 50 gallon tank (smaller sized equipment) or even a 50 gallon All-In-One (with equipment in a back chamber) may free up storage space in the tank stand, give you a more comfortable amount of space to work in, and be a much more enjoyable fit.

Likewise, if you have ample space for a 100 gallon tank, you may find that bumping up to a 120 gallon won’t take up much more room than the 100g while still giving you a fair bit more water volume for fish.

3) How much time — and determination — do you have to care for it?

It’s very important to be honest with yourself on this one…

Nano tanks (under 40g) and pico tanks (5g or less) can be great for small spaces.  And they often take much less time to maintain — after all there is less glass to clean, less water to top off and replace, and less livestock to tend to. But they take constant, unwavering vigilance and care. With such a small water volume, if something goes wrong it can impact the entire tank VERY fast. Miss just one top-off or water change and your tank can crash overnight. Let nitrates get a tad high for even just a day or two, and all your corals and fish can die in a matter of hours.

With medium and large tanks, there is a bit more tank to clean, more water to top-off and change out, and more live stock to tend to. But the larger water volume also means more leniency. If you get a little lax in your care and maintenance, it will take longer for any chemical imbalances to build up in the water — giving you more time to find and correct the problem, and a bit more breathing room when it comes to making mistakes.

4) How simple or challenging?

Many aquarists will strongly disagree with what I’m about to say, but here it is anyway…

Just because smaller reef tanks require more diligence to care for and give far less room for error than larger tanks doesn’t mean you should discount them as your first aquarium.

If you want a lower-risk system that will be easier to learn on and be a bit more forgiving in its care, then by all means start with an aquarium that is at least 50 gallons, if not larger.

However, if you thrive on challenge or prefer to ‘eat your vegetables first’ rather than easing into them — in other words, you want to face all the ups and downs right up front rather than spending time and money easing into them — then you may be better suited to starting small…

If you have a small budget… enjoy challenge… or want to find out whether or not you’ll like the hobby without spending a lot of money, consider goin small.  Just keep in mind you may face more difficult and greater chance for frustration or discouragement.

If you have a larger budget… want more breathing room to learn… or can honestly admit to yourself that you may not have the time or diligence to care for a small tank, then consider starting out with a tank that is 50 gallons or larger.

5) How many fish would you like to have in it?

Many first-time aquarists start with this question when, in reality, they should finish with it.

Let’s face it, if you only have enough room — or enough money — for a 50 gallon set-up, then that’s the biggest tank you can get. And the most fish you can fit in a 50g  is about 4- 5 fish (that are ~3″ long). You don’t have room for a larger tank… and if you try to cram more fish into the tank than the biosystem can handle, you’ll crash the tank and them all.

In other words, unlimited room and money for an aquarium, space and budget will determine your tank size. And tank size will automatically determine then number of fish you can keep healthy and alive in it…

So, choose you tank based on the 4 questions above. Then, instead of selecting your aquarium based on a desired number of fish, select your desired fish based on the size of the aquarium — it’ll save you time, result in a much healthier and enjoyable aquarium set-up, and prevent a lot of disappointment and frustration. Besides, in the end there really is no other choice.

Choosing the right tank size for your first aquarium

You’ve no doubt heard the phrase, “Go big or go home.” Well, in saltwater aquarium circles, it seems to be one of the more common pieces of advice given to newbies just starting out in the hobby. And perhaps for good reason…

A thorough search of popular saltwater aquarium forums and how-to websites will reveal that experienced aquarists often suggest someone new start out with a tank that is at least 50 gallons or, better yet, bigger.  The reason:  increased stability.

A reef is a very complex ecosystem.  A reef in a box even more so. After all, there is a LOT of chemistry and balance continually taking place. Salinity, ammonia, phosphates, nitrates, nitrites, calcium, magnesium, iron, iodine, strontium — many different chemicals and minerals are present. And if even just one gets too far out of balance — either in excess or lack — it can cause anything from unhappy fish and corals to a complete tank crash.

That said, the more water there is in the system the longer it will take for an imbalance to reach critical levels. And that means the more time you will have to (hopefully) detect it.

Bottom line: a small set up — e.g. a nano or pico aquarium — will require much more vigilance and diligence in its care whereas a larger one will give a little more room for error. Hence the suggestion of going with a larger water volume for your first aquarium.

Of course there is a catch with selecting a 50g (or bigger) tank for your first reef aquarium: cost.

Let’s say you’re going with good, new equipment — not top of the line, but good enough that you won’t necessarily have to replace it if you decide to upgrade to a larger tank in the future. For a 50 gallon tank you could easily be looking at $3000+. Bump up to a 100g or 120g set-up you can quickly reach $6,000-$8,000.

And keep in mind, this is just for mid-tier equipment. If you get caught up in the excitement of shiny, new, top-of-the-line equipment you could easily be looking at close to $10,000 by the time your done.

In fact, because the price of a 120g tank was only tiny bit more than the cost of a 100g tank — and would provide much more room for fish and coral — I initial settled on going with a 120g display tank for my first aquarium.  However that was just for the tank itself. By the time I added in a nice stand and hood, the latest and greatest lights, powerheads, pumps, sump, live sand and rock, etc., etc. I was looking at over $8,000 just to dip my toe in the hobby and see if I liked it.

Of course, this was for a dream set-up. I could’ve also gone the route of used equipment instead of new. Lower quality gear instead of high-end gear. Not allowed myself to be seduced by the desire to have fancy tech stuff like a reef controller and modules when old-fashioned test kits would make do. And so on…

The trade-off would have been time, and uncertainty.  It could take many months for used pieces of the equipment I wanted to come for sale on forums or craigslist. And there would be no guarantee it wasn’t abused, damaged, or just so old might it might soon fail.

It was a tough choice: risk a TON of money on a hobby I may not even like… or pay more in the form of time and a higher risk that some of the equipment might fail.

But then I realized there was another option: go small.

Yes, I will have to be more vigilant in monitoring the reef tank. Yes, I will have to be diligent in my care in maintenance of it. And yes, it will be more of a challenge.

But it will also allow me to BOTH have the clean, sleek type of ‘dream setup’ I imagined and do find out if I’ll actually enjoy the hobby for less than $2,000.

And besides, isn’t the whole point of taking on a hobby to embrace the challenge rather than trying to hide from it?

So, when you’re trying to decide what size aquarium to choose for your first reef in a box, ask yourself this…

“What is driving your choice — joy, honesty, and certainty…or a mix of fear, uncertainty, and greed?”