TDS stands for Total Dissolved Solids. Think of it this way...you are driving 60 mph on a motorcycle through the desert and the wind is not blowing. The sky is calm and clear...there would be little to irritate your eyes lungs, skin, mucous membranes, airway etc. Now imagine the same motorcycle and speed, but you are driving through a sand storm......lots of damage, irritation and if left in the environment for very long, eventually death. That is the environment our fish are in when in the aquarium. The more things we add to the tank, (chemicals, salts, minerals, stabilizers, etc) add to the ammount of stuff the fish have to contend with. It is both very stressful and there is no escape. When we add things to the tank, we think we are helping, and in the short term we are...but in the long run we are making things worse. The only way to reduce TDS is through frequent water changes and the elimination of things that contrubute to TDS. Think of it another way...water that is said to be hard has high TDS. Water that is said to be soft has low TDS. Certain fishes like low TDS like Discus, while others can tolerate high TDS, like African Cichlids. There is another water perameter called conductivity which is measured in Micro Siemens, or the ability of the water to conduct electricity. The higher the conductivity, the more stressful it is on fish due to osmoregulation. There is a guy called Joe Gargas who lives near me. He wrote the book on water quality and chemistry. Go to this site:
Aqua Research Center
Joe had a small book there $20.00 that will make you a water expert! You will NEVER have fish or water problems again, because you have a thorough understanding of water and water quality. You will learn what to do and especially what NOT to do. If you are spending loads on dollars on aquarium chemicals, you will stop and save your money. I have not used any chemicals whatsoever in more than 9 months and my fish are doing just fine! As a matter of fact, they are thriving.I have 17 discus and 11 Angels, and they are growing like mad! No disease, distress, death, loss of appetite, eye or skin problems...absolutely nothing. And all I do is 50% WC on my 135 per week, and 80% WC on my 75 per week....no excuses. I can change out 40 gallons of water (40 out and 40 in) in about 15 minutes. No special tools....just a power head and a hose....thats all.