I know it isnt the prefered way to cycle a tank.
But I read somewhere to do a 25% pwc everytime your tank was at or above 0.25 ppm, so 1 to 2 times per day, and your fish would be fine and not that effected by it.
What is the truth to this, what is the pros and cons, ect.
This is misleading. Fish produce ammonia, and ammonia is toxic to all life forms. The longer the fish is exposed to ammonia, or the higher the ammonia level is, the more detrimental it is to the fish's physiology. I have no idea as to your level of knowledge on this subject, so I will copy some bits from an article I wrote a while back that hopefully will make it clear.
Nitrogen comprises about 80% of our atmosphere, and every life form on earth works hard to acquire it. In the aquarium, nitrogen exists in four/five forms: ammonia [NH3], ammonium [NH4], nitrite [NO2] and nitrate [NO3]. De-nitrification (which involves the fifth form, nitrogen gas) will be mentioned below.
Ammonia is a by-product of all aerobic metabolisms—fish, snails, invertebrates, fungi and bacteria; it naturally occurs from continuous biological processes and living organisms in any aquarium, and even at very low levels this ammonia is very highly toxic to all life. At levels between 0.5 and 1 ppm there can be long-term or permanent gill damage. Ammonia is never healthy at levels that can be detected by our standard test kits, and in most cases will have negative effects on the fish. [1]
The fastest uptake of ammonia in an aquarium occurs with live plants; ammonia can be both assimilated (as a nutrient in the ionized form ammonium) and taken up (as a toxin, NH3) by plants. But ammonia is also taken up (though more slowly) by certain nitrifying bacteria, and this produces another form of nitrogen—nitrite, which is also highly toxic to all life at very low levels. Fish readily absorb nitrIte from the water and it combines with the hemoglobin in their blood, forming methaemoglobin. As a consequence, the blood cannot transport oxygen as easily and this can become fatal. At 0.25 ppm nitrite begins to affect fish after a short period; at 0.5 ppm it becomes dangerous; and at 1.0 ppm it is often fatal.
Another group of bacteria take up nitrite, producing nitrate, which is still toxic though much less so. I won't get in to nitrate and beyond, as I think I have explained why ammonia (and nitrite) are still problematical at any level. Thus, daily water changes to dilute the ammonia (or nitrite later) are needed to prevent it building up to even more toxic levels. But the problem is that fish are affected by this, even if they live through it. A weakening of the fish and stress occur, and this means the fish will have problems throughout its life that it woould otherwise not have had to contend with. It will be prone to disease more readily, and in most cases (maybe all) live a shorter lifespan than normal.
Byron.
