Hello dear community,
Hardly any maintenance measure in reef aquariums is discussed as controversially and yet as routinely as water changes (WW). The old rule "10% per week" is often heard. But is this really still appropriate? Or is it an outdated routine from a time when we knew much less about our tanks?
In this article, based on the detailed explanations of the SANGOKAI recommendations (SEA-Z), we want to critically examine the role of water changes and find out when it really makes sense – and when perhaps not.
A look back: The changing role of water exchange
The Grounds for water changes has changed significantly over the decades:
- 70s/80s: Aquariums were often heavily populated with fish, and the filter technology was less powerful. The WW primarily served Dilution of pollutants and nutrients such as ammonium and nitrite [Source: SEA-Z, ~p. 151, pts. 2408-2409].
- 90s/2000s: With the advent of stony coral care, the focus shifted. It was hoped that the WW would be able to Trace elements and minerals [Source: SEA-Z, ~p. 151, pts. 2409-2410]. The knowledge that was was supplied accurately, but was limited.
- Today: Thanks to modern laboratory analysis (ICP-OES, etc.), we can assess the condition of our water much more accurately. WW is now moving more into the role of a measure to restore or maintain the Ion balance and to Removal of specific contaminants [Source: SEA-Z, ~S. 151, pts. 2411-2415].
Myth of pollutant dilution? The (in)efficiency of WW
Sounds logical: Water out, pollutants out. But the math shows limits. A water change only dilutes the water. Let's assume you have 50 mg/L nitrate and use 20% water:
- After 1st WW: 40 mg/L (10 mg/L removed)
- After 2nd WW: 32 mg/L (only 8 mg/L removed)
- After 3nd WW: 25,6 mg/L (only 6,4 mg/L removed)
To really drastically reduce the value, extremely many or very large water changes would be necessary [Source: SEA-Z, ~p. 154-156, p. 2463-2485]. Conclusion: For acute halving a very high value, 3-4 WW at 15-20% each at short intervals may be useful. As a long-term solution for a basic Problem (e.g. nutrient source in the tank) the WW is inefficient and expensive. Investigating and eliminating the causes is crucial here!
Myth of trace element supply? WW as a supplier
Many hope to replenish "used" trace elements with water. SANGOKAI takes a critical view:
- Loss of valuable substances: With each water change you also remove important substances that are already present in the tank (calcium, potassium, etc.) [Source: SEA-Z, ~p. 158-159, points 2535-2541].
- Unknown salt quality: Do you know exactly what is in your salt really is in it and in what concentration? Does it contain boron? Is the strontium dosage correct? Poor or inconsistent salts can cause problems rather than solve them [Source: SEA-Z, ~pp. 152-153, points 2427-2453].
- No targeted intake: WW is a scattergun approach. If only potassium is missing, you'll still be replacing dozens of other substances – inefficient and potentially disruptive [Source: SEA-Z, ~p. 163, points 2621-2623].
- Inconsistent supply: Corals and microorganisms have a daily Demand. A weekly WW cannot adequately cover this demand [Source: SEA-Z, ~p. 163, points 2615-2617].
Modern alternatives such as targeted supplementation based on analysis are usually superior here.
It's the salt that matters: quality and the tricky ion balance
A central point in the SANGOKAI recommendations is the Ion balance, i.e., the correct ratio of the main components (especially sodium, chloride, sulfate, magnesium, calcium, potassium) to each other and to salinity [Source: SEA-Z, ~p. 165, pts. 2654-2663]. This can be disturbed by:
- Bad sea salts: The most common cause! If the salt itself is mixed incorrectly, no amount of water will help [Source: SEA-Z, ~p. 170, pts. 2738-2746].
- Unbalanced supplementation: Methods such as “classic balling” without the originally intended mineral salt balance lead to an increase in sodium and chloride due to the addition of CaCl2 and NaHCO3. If the resulting increase in salinity is corrected with osmosis water, all other Ions (potassium, magnesium, boron, strontium, etc.) are relatively diluted and are permanently lacking [Source: SEA-Z, ~pp. 172-173, points 2778-2801]. A regular WW of approximately 10% per week can partially compensate for this, but is not the most elegant solution [Source: SEA-Z, ~pp. 173-174, points 2808-2814].
Important: Stay with high-quality, laboratory-tested salt! Constantly changing different salts, as was often done in the past, leads to unnecessary fluctuations and complicates troubleshooting [Source: SEA-Z, ~pp. 159-160, points 2542-2578].
When is a water change advisable? SANGOKAI recommendations:
Despite the criticism of the routine, there are situations in which a WW is clearly recommended according to SANGOKAI:
- Acute problems: In cases of poisoning, severe contamination or unexplained mass deaths, a large (possibly multiple) WW is often the first emergency measure [Source: SEA-Z, ~pp. 156-157, points 2499-2501].
- Serious ion imbalance: If a laboratory analysis reveals massive shifts in more main components (often caused by bad salt), a series of WW (e.g. 3-4 x 15-20% every 2-3 days) or a very large WW (up to 100% with tested NSW or top salt) can help to restore the balance [Source: SEA-Z, ~p. 168, pts. 2706-2719].
- Starting phase with artificial rock: Some ceramics, cements, or dead rocks may initially release substances such as silicate, aluminum, lithium, or heavy metals. In these cases, regular water removal (e.g., 10-15% weekly) is recommended for the first few months to compensate, accompanied by laboratory analyses [Source: SEA-Z, ~p. 156, pts. 2490-2498; pp. 176-177, pts. 2858-2864].
- Physical cleaning: When sludge and detritus are sucked out of the sump or substrate, water is inevitably removed, which must be replaced [Source: SEA-Z, ~p. 176, pts. 2847-2848].
When is a water change (earlier) not the best solution?
- As a pure routine: In a stable tank that is specifically supplied (e.g. with balanced methods such as SANGOKAI BALANCE) and whose values are confirmed by analyses, routine water change is often unnecessary and even carries the risk of disturbing the optimized water chemistry [Source: SEA-Z, ~p. 174-175, points 2821-2826, 2840-2842].
- For targeted correction of individual deficits: If only boron or potassium is missing, the direct dosing of these elements is more efficient, faster and cheaper [Source: SEA-Z, ~p. 165, points 2645-2646; p. 169, points 2721-2727].
- For sole N/P control: Elevated nitrate or phosphate levels usually have a cause (overfeeding, rotten spots, inefficient filtration, etc.) that needs to be addressed. Water treatment only treats the symptoms.
Conclusion
Water changes are a tool in our toolbox, but not a panacea or an unavoidable obligation. The SANGOKAI perspective clearly shows: Understand instead of generalizing!
Modern analytics and targeted supply systems allow us to control our water values much more precisely than ever before. The focus should be on Constancy, quality (salt!) and needs-based adaptation A water change can be very important in specific situations, but the blind "10% per week" routine has become obsolete in many modern reef aquariums.
Know your system, use the analysis options and make informed decisions – your reef will thank you!
What are your experiences with water changes? Share your thoughts with us in the comments!
CommunityCorals
