Water changes definitely work—don’t get me wrong. But I think we often overlook some important math. When you perform a 33% water change, you're only replenishing 33% of what was consumed during that time. The new water gets diluted into the existing water, which means each subsequent water change becomes slightly less effective. Over time, this dilution effect adds up. That’s why dosing macro and trace elements eventually becomes necessary. Personally, I believe this dilution is what led to the dreaded “old tank syndrome” back in the day—before automatic dosing systems became the norm.
I had AI do the math (any mathematicians out there want to verify this?)for what it would take to change 100% of the water in a system doing consecutive 33% water changes (keep in mind this does not factor time between water changes when more depletion of elements occurs) and this is what it came up with:
Thank you Seth it. Is much appreciated.
Another thing to consider would be the brand of salt. They all have different ratios and there are pluses and minus to every salt. For example, I’ve used reef crystals for probably 15 years. Great salt. Consistent. However, alkalinity is always high. Therefore if you did too large of a water change, you would swing your alkalinity. Every salt has a different trace element ratio as well. I’ve done ICP on over 15 types of salt and none of them are perfect. Therefore, if for example you do say a 33% water change with a salt mix that has low fluoride and strontium, high calcium and iron, is the waterchange benificial? In some ways, possibly…. if you are trying to dilute nutrients, but if nutrients are good, you may be actually hurting the system in my opinion. Personally, and this isn’t the cheapest way to do it, but I take an ATI-MS ICP test monthly and add a trace element solution to dose daily (on the hour). A water change can become almost obsolete unless there is physical debris that needs to be removed or nutrients need to be kept in check. There are some salts that I feel have a better trace Than others. Tropic Marin pro (low Kh, but can be adjusted before the waterchange), Red Sea blue (but has high silicates) and two little fishies Accurasea, which in my opinion has the best macro and micro element ratio. It isn’t perfect as it can have a little bit higher of an aluminum content, but if you are using kalkwasser, it seems to be a non issue. However, coming back to the original topic, if you choose a salt mix with a very good element ratio that you were striving for along with a trace element solution that you dose, I have done up to 80% water changes with zero issues. On the other hand, even salt with unfavorable micro traces can be used on a percentage basis, say five or 10% with very little impact.
Great info Steve! Thanks!!
If you were to take what it says here and apply it to your reef keeping , would you say that 50 percent would be to large of a change weekly, biweekly? And on a nano of 25g or less , start dosing all for reef to maintain healthy levels or would you still have to add some traces in your experience/opinion?