The thinking behind this is a bit misunderstood, though there is validity. Plants during photosynthesis (which is driven by light so occurring in daylight) take up CO2 as a macronutrient. Oxygen is a by-product and is released through the roots (primarily) and leaves. At the same time, plants, like fish and some bacteria species, are respirating "normally," taking in oxygen and releasing CO2. This respiration is 24/7 regardless of anything else. The CO2 taken up during photosynthesis is considerably greater than what is expelled through respiration. So during daylight, all this causes the CO2 to diminish, and the pH will usually rise slightly.i heard that plants also absorb alot of oxygen leaving the fish with less oxygen bit thats something i will research soon
During darkness, the photosynthesis ceases. Respiration continues normally, though with fish at decreased levels because they are not as active (unless nocturnal species). In very heavily planted tanks, or tanks with too many fish for the biological balance, oxygen can become depleted and CO2 increase accordingly. The easy way to deal with this, in addition to not overloading the fish, is to have good surface disturbance. This can be continuous, day and night. In high-tech planted tanks where CO2 is being added by diffusion to boost the plants, these units are turned off during the period of darkness, and sometimes additional aeration is provided to ensure a good exchange of oxygen/CO2 at the surface. My tanks are all planted, with thick floating plants, so I simply ensure there is surface disturbance 24/7 and I have had no issues.
Nothing is a beneficial as a partial water change. And you cannot change too much water. The aim of these changes is to ensure stability in the water chemistry. This is another advantage of selecting fish suited to your source water parameters--water changes are not a problem, ever. A biologically balanced tank will establish a fairly stable chemistry; provided water changes are regular and substantial, this is not going to change. Now, we are assuming the parameters are relatively close; GH, KH and pH should be much the same [another reason why adjusting these for specific fish is problematical], and temperature is easily controlled manually at the tap. Slightly cooler fresh water is usually advisable as it stimulates fish, frequently into spawning, since it replicates the tropical rainstorms. Of course, if one is again messing with prepared water the temp can be an issue.The reason i ask, is i heard that a massive water change can have a bad effect on the fish such as temperature and basically the fresh water,
Note: The only exception here is if you ignore the tank long enough for the biological system to fail, such as an overcrowded tank or overfed fish with no water changes. Even here, a major water change is beneficial, except if the pH has become acidic in the tank and the fresh water pH is above 7. This sudden influx of "basic" pH water can cause the tank pH to rise above 7, and the problem with this is that the ammonia in the water which was ammonium in an acidic pH and thus not toxic, immediately changes to toxic ammonia, often killing the fish within minutes.
Filters need regular cleaning and this too impacts stability. The brown gunk that accumulates is organics and these need to be controlled. This is a main cause of nitrates, and nitrates are toxic to all our fish so keeping nitrates as low as possible is always best.would it.be useful to clean my canister completely, then refill, then do my 75% change and replug everything and use some of the water in the filter ?
My tanks all have internal sponge filters, except for the 90g which has a canister. The sponge filters I rinse under the tap at every water change. The canister I clean every couple of months. This tank is way under-populated so I don't worry too much; the buildup of organics in the hoses which can noticeably slow the water flow is what usually triggers a filter cleaning. But regular filter cleaning/rinsing is important most of the time.