Okay thanks for the info. Before the fry my weekly water change was keeping the tank good. I will probably increase it to 25% two times a week when I get my python just to help the fry grow.
You may have a misunderstanding about water changes like many others initially. The thinking that "my weekly water change was keeping the tank good" is probably false. And doing two 25% water changes is not as effective as one 50% each week. Now I'll try and explain these.
Fish impact water in many ways. Releasing ammonia and excrement are the two most aquarists recognize, but there are others. Fish also release pheromones and allomones; these are chemical signals that other fish can read, and some of the signals can cause stress to other fish. Filtration does not do much with all this "pollution." Ammonia can be used by plants and bacteria, but that is about as far as it goes.
The breakdown of solid waste leaves pollution in the water. No filtration can fully deal with this. No filtration can begin to deal with the pheromones and allomones. Live plants can help, but the fish load to water volume and plants would have to be so small for this to work effectively that we might as well assume nothing is going to deal with such pollution. Except water changes.
Water is continually passing into fish via osmosis through the cells and gills. Fish release copious amounts of urine which is not the ammonia as it is with land animals but the urine is "dead water." Eventually the fish are swimming around in nothing but dead water. At the same time, the pheromones and allomones continue to increase, and this stresses out the fish.
In their habitat, the ratio of fish to water volume is immense by comparison to the largest aquarium. And the water in nature is continually changing; this involves the passing of water downstream in rivers and streams, or vertical circulation in lakes, as well as rain and snow melt. Fish live in the same water for no more than a second. There is absolutely no way to even come close to this in a closed aquarium unless you have continuous flow-through of fresh water. Even most public aquariums cannot achieve this. The water change is the only method.
The longer fish remain in the same water, the more detrimental it becomes, for their physiology, metabolism, lifespan, health...everything. So the more water you can change the better.
Which brings me to the amount. When you change say 10% of the tank's volume, you remove 10% of the pollution, leaving 90% behind. The next day, fish have added more pollution. If you change another 10%, you are then removing 10% of the 90% that was left plus the new pollution added since the previous day. So even with these water changes, the pollution is continuing to increase from day to day. Doing a larger change like 70% once a week will thus remove much more pollution week by week that the much smaller daily changes. This doesn't have to be extreme, provided you do not overload the fish, don't overfeed (more in means more out), have live plants, and ensure the fish are all truly compatible because this lessens their impact biologically.
Using test results like nitrate to determine when a water change is necessary is therefore pointless, as by the time the nitrates have risen the damage is being done, and this is irreversible. Only a regular routine of adequate water changes can improve the health of the fish. Provided the parameters, being GH, KH, pH and temperature, are reasonably close, you really cannot change too much water. But changing what is adequate and sufficient for the specific aquarium is all you need.