Water turbidity can occur for many reasons. Waste saturation (too much food, fish excrement), poor oxygenation (too many fish to a certain volume of water, too weak a filter), can be of mineral origin (tiny particles that may be present in the pebbles used as a substrate), anything limestone origin (dolomite stone, decor for marine aquarium eg shells and the like). It can also be caused by the “bloom” of the bacterium, which is related to the amount of waste in the aquarium. Waste breakdown bacteria use large amounts of oxygen, causing fish poisoning with CO2.
For goldfish, filtration must be much higher than that for tropical aquariums, because in aquariums with gold fish is hard to preserve plants because gold fish love to eat them, which means that you can never complete the natural cycle of substances that are produced as a by-product of biodegradation of waste. This leads to imbalances in water parameters, as well as poisoning to which sensitive organisms, such as bottom fish and shellfish, respond first.
Aqua safe is a means of basic water treatment, ie. it release the binding of harmful substances and the binding of free radicals and ions such as chlorides, which are highly toxic to fish. Crystal Water can help if water is turbidity, but can not completely resolve it, if it is of biological origin. Use Vital after switching off the light because the B complex vitamins are denatured in the presence of light. Esay Balance is an agent that regulates several basic parameters in water. If you have a large enough filter chamber, put in some activated carbon. Keep activated charcoal for a few days, monitor the condition and replace it if the water has not yet cleared completely.
Try with purigen, which is a filter medium. Another solution is of a slightly more sensitive nature. It is about dosing H2O2, ie. of hydrogen peroxide. Very small doses are given, up to a maximum of 1 ml. Hydrogen peroxide will eliminate some of the organic pollution because it will oxidize, it is completely harmless to fish if used carefully and decomposed into pure oxygen and water. Try to starting with 0.1 ml. You can try to use use several of these methods, not just one.