I've read conflicting opinions on that fact. Some people believe that as long as I leave the filter media intact I shouldn't have to completely cycle the tank. I might have a mini cycle but it should only last a few days and with so many plants I might not have one at all.
This is something I concur with. As long as you hav a filter that has been runing for some time and the tank has been cycled and running for while as well means that the filter media will have lots of the beneficial bacteria thats needed.
Plus the fact that having a number of plants will also help with the ammonia / nitrite levels as well does indeed contribute to this.
So changing the substrate can be done wihtout having to worry too much about the cycle provided the filter and plants are left alone and not cleaned. Amini cycle MAY occur but as long as keeping an eye on water parameters and if needed, a water change will help lower levels until things stabilise once more.
Changing the substrate is a messy job no matter how it is done to be honest.
There are several methods to doing this, such as moving the fish and shrimps etc to a temporary tank or container that has a heater and filter at least and then doing the changeover of substrate in the tank you want to do. That way theres less stress but having said that, moving fish and shrimps is very stressful for them anyway!
Another method, this is what I have done in past with small tanks as 10 gals, is to use the syphon hose and bottle method.
(You may do this if the gravel is small and light thats best, but if large gravel then would not recommend this.)
Remove the plants and put in some tank water in a container, then remove an area of gravel substrate via syphon hose into a bucket or container, keeping a close eye on the water level and end of syphon hose to ensure no fish or shrimps gets sucked up as you do this, then to replace the substrate using the bottle method, fill up a clean plastic 0.5l or even a 1l bottle with the sand you want (remember to rinse off the sand well before adding to tank) and simply fill the bottle sand and top up up with water then turn bottle directly upside down in area where substrate was removed to let the sand fall out, (this has a couple of benefits as it will not create such a mess and will at same time suck up any dirty water) once sand is out of bottle then quickly turn bottle right way up and out of tank, a little practice makes this method worthwhile doing.
This may require several times to remove all the substrate and adding of sand to your satisfaction. This method is not really worth trying on larger tanks than 10gals as it would require a lot more time and work etc.
Really, its down to a preference as well as how much you want to do with the tank with which method you want, the moving of fish to another temporaray home gives you more time to set up the tank exactly the way you want things and moving and replanting the plants and decor means you won't worry so much. The syphoning of gravel and adding sand via bottle is quicker but mistakes can be easily made and potentially more stressful to the fish.
But whichever method you try, do ensure you fill the tank with clean dechlorinated, temperature matched water.
Do be aware whichever way is stressful to the fish and shrimps so take your time doing this and do not do fast or jerky movements to further spook them out.
