Originally Posted by
afriend
Larry,
Thank you for your organized, detailed and well prepared post on this subject. I find it very refreshing that yours, and all of the other posts to the OP, are positive and helpful. Usually when the subject of why large water exchange is necessary, there are comments like "just make large water changes because that is what works and KISS (keep it simple stupid)". I happen to be one of those people that wants to know why, and I believe that understanding is one of the keys to success in life. For many years now, I have advocated that the primary reason for water changes and tank maintenance is to reduce the amount of organic compounds that pathogens feed on and thus reduce their numbers.
I would welcome your comments and thoughts on two my observations of your post:
Why not include all forms of pathogens, including bacteria, virus, parasites, and fungus?
My understanding is that there are less pathogens present in lower PH water and that most of them are completely different than those at a higher PH.
I would like to offer some additional information that may assist in understanding why discus require large water changes:
1) Many of the strains of discus available today have evolved in water with a low PH for thousands of years. As such their immune systems (which is determined by their DNA) have adapted to the quantity and types of pathogens (bacteria, viruses, and parasites, and fungus) that are common to their native habitat. It turns out that water with higher PH has not only many more pathogens, but also a different type. Thus fish that are kept at a higher PH are much more sensitive to attack from unfamiliar pathogens. Young discus are especially vulnerable because their immune system will develop and adapt as they age.
2) Another important consideration results because discus are quite sensitive and become easily stressed. Stress can be caused by changes in water parameters (PH, TDS, ammonia, nitrite, and nitrate), temperature, lighting, motion outside the tank, pecking order, and other factors. Water that is not biologically clean also causes stress. When discus become stressed, they often become lethargic and refuse to eat. When this happens, their immune system weakens and they are much more subject to attack from pathogens.
Paul