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Mark Porzilli's avatar

THANK YOU for this piece, Steven. As always, it's so well written and so full of imagery, one can just 'see' the house flooding! (Yes, 'been there, done that'!) I could say this about all of your articles. But this one in particular hit a nerve for me. All one need do is peruse any aquarium forum where planted tank enthusiasts boast of literally "never having to change water". I cringe at the thought. Inevitably, the reasoning asserted is "nitrates". That is, "the plants consume the nitrates and well, we're done!" The Nitrogen Cycle is completed in our little glass box. But is it? Are nitrates the entire story? I was so pleased to see your article detailing why water changes are essential. There are so many reasons because there are so many toxins beyond nitrates that require removal. If I may expand briefly, let's assume you have enough plants to consume 100% of the nitrates. Good start. But when organic material decomposes, it forms far more than nitrogenous toxins. OK, let's assume your cycled filter is eliminating 100% of the ammonia and nitrite, and your plants are eliminating 100% of the nitrates, excellent. But the phosphates, also a product of organic decay build and continue to build. Let's take this further. Darwin 101. Fish secrete hormones as a form of dominance. Larger fish secrete hormones that inhibit the growth of smaller fish in order to dominate the gene pool. It has widely been observed that mixing fishes of varying sizes can stunt growth of the smaller fish while the dominate fishes grow to maturity. In fact, GIH or Growth Inhibiting Hormone secretion is considered a significant issue in breeding discus in particular. Parallelism. Bacterial counts build over time in the water column. Cloudy water is often from bacterial blooms of heterotrophic bacteria. This competes for nutrients with nitrifying bacteria and the latter, reproducing at a fraction of the rate of heterotrophs, sees compromise. Mysterious nitrite or ammonia spikes etc. And all of these bacteria are aerobic, so dissolved oxygen is reduced. And these are merely the additive detriments. Depletion. The fish and the bacteria require minerals for health and reproduction. Of particular import being calcium and magnesium. As these are consumed, the "never changed water" mineral content is depleted. Calcium is required for growth and magnesium for digestion, amongst other reasons. Calcium is essential for nitrifying bacteria to reproduce as well. An ichthyologist friend of mine swears by remineralization for long term health of her fish. No, I cannot get on board with the "never change water" crowd any more than I would want to live without a clean water supply in my home. There are simply countless reasons we need fresh, clean water daily. Humans and fish alike. Thanks again for the terrific article!

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