Water change
 

I know this is a crazy question but I want to be clear. When I do water changes using Tetra safe do I add the product to the water BEFORE I fill the tank back up OR do I do the water change and add the product. I have a 35gallon tank. Thanks!

I would say treat the water in the bucket before adding it to the tank, as if the chlorinated water hits the filter media it could/will kill off the beneficial bacteria that lives there. not worth the risk.

Thanks I figured that would be the best thing to do.

The safest, best way is to condition water with the appropriate amount of conditioner before it goes into the tank.
Having 'said' that, many people here that use a Python or similar hose device for water changes report that they add the appropriate amount* of conditioner to the tank, then fill with the hose.
* The wrinkle is in the 'appropriate amount' - some use an amount for the whole tank, while others just use the amount sufficient for the new water being added.

I have sumps on my 75g and 180g tank and I add the conditioner to that before filling the tank, then I turn the pump on so it mixes before going direct to the tank.

I have a siphon hose that I am using to take out about 25% of the water into a 5 gallon bucket. Then I thought how the heck will I know how many liters/gallons I'm putting back in so that I can treat the water accordingly. But I'm def gonna get it straight before Wednesday! Scheduled water change. I know with experience I can just KNOW but for now I'm going to rely on these instruments lol

Well 25% of a 35g tank is 8.75g, so we could most easily round this to 10, so fill your 5g bucket twice, then fill with tap water at tank water temperature (76-78F), treat with conditioner and refill twice. :-)