Write-Up Wednesday: Water Changes


Water changes serve an important role in your tank, yet you either love them, or hate them. I’m in the “love them “camp and when I’m designing a tank for a client, I’m often asked to make water changes as easy as possible.

The main role a water change plays is to export nutrients out of your saltwater tank. By removing existing water out of your system and replacing it with fresh saltwater, nutrient levels are reduced and other important levels (calcium, magnesium, trace elements, etc) are increased. Here’s the key thing to note about the reduction of the nutrient levels though: unless a large (50% or better) water change is performed, you’re not going to reduce nutrient levels by a large amount. I often see people post about having a high phosphate or nitrate levels and the advice given is to a 10-20% water change. The water change won’t hurt and it isn’t going to provide the large drop in levels that the person is likely looking for.

Why even do water changes then if they aren’t useful unless the quantity of water removed is large? Several reasons:

  1. Replenishment of elements. Until a tank is well stocked with growing (emphasis on growing) corals, calcium, magnesium and alkalinity levels can be maintained simply through water changes.
  2. Good habits. When you are doing a water change, you have to pay attention to your tank as you are turning pumps on/off, removing water, etc. The water change exercise is a great time to look over your tank to make sure everything is looking good and running well. Maintaining a weekly water change routine forces you to give your tank a good look over which will help catch any problems faster.

Of course people always ask if they can never do a water change and still maintain a saltwater tank and the answer is “yes”. Some tanks do fine on zero water changes. I’m not a fan of the zero water change method as I enjoy water change days and all the hands-on-the-tank activities that come with it. As I write in all my books, there are many ways of setting up and maintaining a saltwater tank. My way isn’t the only way and it is the way that has worked for me and my clients time and time again.

Browse the Store! Questions?

Comments for this article (14)

  • Bryan says:

    I just started changing a gallon a day on my 90 gallon system. I was doing 15 gallons every two weeks. With a gallon a day, I hope to get the same benefits as I was getting, while at the same time, the change is faster and easier since I only replace a gallon at a time verses 15 gallons at a time!

  • Matt says:

    I don’t mind water changes but would love if there were a proven method of automating the process,since I have several pets to care for.

    Does anyone know of such a thing or video demonstration?

  • Damion says:

    My friend setup a dual headed peristaltic pump to do automatic water changes. 2 gallons a day, no frigging buckets! Automated. A barrel of sw in the garage and dump the old sw down the drain.

  • Jeff Wagner says:

    If you have a controller like an Apex, you can easily create a robust and safe auto water change system. Yes it can be a little expensive but I have personally never looked back after purchasing my controller. It makes everything so much easier and gives you near limitless flexibility. There is many brands out there and I would recommend anyone with the resources to look into one. It can be done without a controller as well. For me though the controller makes it easier and safer.

  • wes thompson says:

    I have a 65 gallon reef tank all though im not a huge fan of water changes I consistently change my water every two weeks 20/25 gallons not only does it give it a cleaner look but my corals are thriving my frog span in particular , so needless to say its a love hate relationship but well worth it. 🙂

  • mike gosselin says:

    I think this is a real good setup for doing water changes this is what I am going to use on my tank when I set it up it is called GENESIS REEF SYSTEMS. they have a unit called the RENEW™ this is a Automatic Water Change Systems and another unit you can buy called the STORM that is a AUTO TOP OFF module it might be a little more expensive but I think its way worth it the RENEW and the STORM in a bundle costs $979.99 +tax + Shipping or you can buy them separate the RENEW has 2 units the Basic and Pro units the Basic costs $499.99 +tax +S-H and the Pro costs $599.99 +tax +S-H. And the STORM has 2 units the Basic unit costs $299.99 +tax +S-H and the Pro unit costs $399.99 +tax +S-H if you get both the renew and storm together they work with each other like when you are doing a water change the renew Automatic Water Change Systems tells the storm auto top off system not to turn on till the water change is done doing a water change. you can see them both at http://www.genesisreefsystems.com or see a few videos on youtube

  • The plummer says:

    Mark, I appreciate what you are doing for the hobby as a whole, and I consider you an expert. I would like to challenge the notion of the importance of water changes. Sometimes I believe this is propaganda from salt producers to sell more salt & promoted by the “herd mentality” experts in the industry. Without challenge there will never be new technology developed. I’m more of a tank dabbler, of sorts and kept fish only with a wet/dry nitrate production facility back in the 90’s. Always in nitrate phosphate danger. Additionally, I was constantly dealing with loss due to ick breakouts. I spent a small fortune in “Red Sea” salt trying to maintain the tank parameters. I finally gave up after four years.

    Two years ago, my children convinced me to set the system up again. This time, I did massive amounts of research and decided to try FOWLR. I had one ick breakout, and determined to QT with 72 hour tank changes.

    I started to have the same nitrate issues as before, then made a remote deep sand bed. I’ve added chaeto in my sump. I haven’t done a water change in 18 months. All testable parameters are zero, and PH maintains a constant 8.4. Calcium is the only additional thing that I replenish, that and when my yellow tang starts to dull in color, I add reef essentials.

    I’m not saying it’s for everybody, but it can help reduce expense and maintain more stable parameters.

  • Asif Iqbal says:

    The deep sand bed is a phosphate sink and will eventually need to be replaced once it is saturated. How long depends on the bio load and how much you feed.

  • Mohamed Alnuaimi says:

    http://www.genesisreefsystems.com/
    Great system, I have been using this system for three month now, it is the best automatic water change. I do 48g a week for my 240g tank.
    Every thing done automatically, I have 300g salt water ready in my store enough for 6 weeks. You can setup the system to do automatic water change daily, last month I was out the country for one month, came back & every thing went perfect .

    Very stable system.

  • The plummer says:

    Asif, I agree, but note I said “remote”. Maybe I should clarify. I prefilter and protein skim 100% of my water BEFORE it enters the remote deep sand bed (RDSB). This should nearly eliminate the phosphate sink, as the deepest part of the RDSB water is acedic and causes the aragonite sand to disolve. Hence, needing replacement sand, though I have not needed to do so, as of yet. It’s been online for two years now.

  • Steve-O says:

    As an engineer myself, I find the genesis system to be a bit over engineered. The system uses buckets and sensors to accurately measure pump output. I can only assume that this system does a good job. But it would seem to me that a dosing pump and a controller could accomplish the same accuracy, without all that extra bulk. Not sure how long a typical dosing pump would last with heavy use, but I’m thinking about trying the DOS pump from Neptune Systems with an Apex controlling the show. Anyone using the DOS yet for automatic water changes?

    I haven’t done an H2O change in 6 months and all water parameters are in check. But I’d be quite interested in doing them, if they did them, themselves.

  • john camping says:

    I currently have a ro/do .. Do I need marine salt or is instant ocean sufficient to use to replace the nutrients? 55gal.. Small wet/dry .. I am worried about nutrient replenishment.. And currently all fish are in QT because of ick outbreak.. Still waiting 60 days for darn ick to cycle.. Uggg.. Jan31.. Going to re introduce the fish back in DT.. They are copper and melafix treatment.. At moment.. Do I need to do weekly water change in QT tank.. 2 dansels are permanent residence there.. Fish only no.. Sand.. Help..needed don’t like seeing my guys die.. Thanks all and happy new year

  • onecansay says:

    I have a system with a total volume of 65 gallons of water. I have softies, lps and easy care sps. My sump is a simple three and half chamber setup. The first is where the DT water arrives. No filters. Under/over to the main chamber which houses the protein skimmer and chaeto separated by an acrylic divider with holes on the bottom half. Then an over/under to the return pump chamber. Floss and carbon in the over/under compartment. I have a DIY bio pellet reactor grabbing water in the first under/over. Chaeto grows and pellets slowly recede over weeks. I change 3 gallons every two weeks. I auto dose all three main elements. Nitrates always 0 and P04 never exceeds 0.25. Most weekly checks @ 0.00. Water is clear. 3 times volume through sump with vortech pumps for DT flow. Everything growing and healthy. As the boss says, know your tank personality and DO NOT LET THINGS SLIDE. Learned long ago you cannot change, you can only manage and maintain. Happy Tanking.

  • Anthony says:

    Using an Apex system with solenoid valves one for ATO the other to fill a mix tank. ATO has a line running from the RO-DI water filter in the garage with a float switch in the sump, need water? kicks on the solenoid till it’s topped off. Put a TEE in line with a check valve from the mix tank, 2 pumps in the mix tank one for mixing other for transfer, drain pump in the sump, pump out from sump, pump in from mix tank. currently not set to run auto, but could just by going to auto mode. Oh yeah float switch on the mix tank, when its time to mix up a new batch of salt water hit the switch turns on the other solenoid, fills to float switch, mix pump runs constantly. The Apex was less expensive and can do a lot more.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.