Question: Tank Set Up

Hi....Devo has been with me now for about 2 months and all going well. I do however want to improve his home and do quite a bit of aquascaping.I currently have a fine black sand substrate and PVC pipes for hide outs as well as live plants that are well anchored. Im using an internal filter and changing app 10 - 20% water weekly. PH is slightly high at about 8.0. I have also added quite a lot of what I would call river stones (large) ....these are mainly white.

I have some ideas for future aquascaping so I need some questions answered as much of the info I track down seems to be contradictory. So, any info will help...

1. Is black slate ok?
2. Do white stones raise PH?
3. Is fine black sand a good plant substrate?
4. How long can an aquarium sit before it needs an empty and a complete clean? Or is this never? (assume I will be changing 10% water weekly)
5. What rocks can not be used? And what can?
6. Should I move Devo when removing and adding components (major changes inc new hideouts, rocks, shifting substrate etc)

Thanks

Johnny

1&2. Slate is usually considered ok. What I do to make sure any rock I'm unsure about is ok, is to put it in a bucket of water for a month, and test the water to make sure it doesn't mess with my ph.
3. Sand is a great substrate for axies, and plants
4. You should do a 20% waterchange weekly if that keeps your nitrates below 40 ppm's. If a 20% waterchange doesn't keep the nitrates below 40 you should do a larger waterchange, or do 2 waterchanges per week. Seeing as your keeping plants nitrates may not be a large issue, but I still recommend at least a 20% waterchange a week.
Also you should do some research on beneficial bacteria, and the nitrogen cycle. Doing a 100% waterchange is usually not recommended for many reasons, but this also pertains to cleaning out your filter. I've heard of a few cases where people killed off their cycle by taking out all their filter media, and taking 100% of their water out of their tank and cleaning off all the ornaments in an attempt to clean their tank. Just want to make sure you don't accidentally attempt to "clean" your tank and kill off your cycle.
5. Rocks that leach minerals into the water are usually not a good idea. Rocks such as limestone will raise your ph.
6. I personally don't move my axolotls out of the tank when moving stuff around, but if you feel more comfortable moving stuff around without Devo in the tank then it shouldn't be a problem

Just in case you don't know about testing your water, you should have an ammonia, nitrite, and nitrate test kit. Keep ammonia/nitrite at 0, and nitrate below 40. If the ammonia is above .5 ppm's, or nitrite above 3 ppm's do waterchanges until the readings have lowered to a safe level.

Thanks...seems I have most of this under control although I've only been testing PH levels. Ill get onto that.