Hi all,
Depends on how you define "too clean". You can certainly do enough cosmetic cleaning to compromise both water quality and fish health.
Against this you don't want to have lots of organic waste in the tank as this will contribute to the BOD (Biochemical Oxygen Demand) and this may remove enough dissolved oxygen to interfere with the ammonia - nitrite - nitrate conversion.
The important factor to remember is that if BOD is reduced, nitrogen conversion is enhanced. (You can skip the next bit if you aren't interested in the chemistry).
Aerobic decomposition of organic material
Oxidizable material + bacteria + nutrient + O2 → CO2 + H2O + oxidized inorganic such as nitrate (NO3) or (Sulf(ph)ate) SO4.
Nitrification
One of the most significant oxygen utilising processes is in “Nitrificationâ€, the biological oxidation of ammonia (NH3) to nitrite (NO2-) and then nitrate (NO3-).
NH3 + CO2 + 1.5 O2 → NO2- + CO2 + 0.5 O2 → NO3-
Note all the "O2" in the equations, that is your oxygen.
Once we've got past obvious organic waste (faeces, un-eaten food, dead fish/plants/shrimps etc), unless we have a planted aquarium nitrate levels will rise, so we need to change some water, this also removes some of the DOC (dissolved organic carbon). I like to change about 10% a day, although it doesn't have to be a small regular water change as long as you are changing about 100% of your water every 10 - 14 days (probably best not too do all 100% in one go).
Once you've done this after that it is entirely up to you how "house proud" you are. I personally like some snails (particularly MTS), DOC, mulm and "biofilm" (algae) and an undisturbed substrate. I want stability much more than I want cosmetic cleanliness. I also try and avoid putting my hands in the water, and I clean the external front glass with dilute vinegar rather than a stronger cleaner.
All my tanks are planted, but I do very little gardening, and no routine algae cleaning from the plants or back and side glass. I think the biofilm development helps with tank stability and also in providing feeding opportunities for fry. I also try to leave the substrate undisturbed (so no poking the syphon in it). If you don't have plants or MTS, you may have to clean your gravel every month or so.
If you are cleaning any rocks, bog-wood etc on a regular basis, or cleaning the whole tank regularly and particularly if you are using cleaning products (detergent, bleach etc) on filter bodies etc or dipping your plants in potassium permanganate or spraying dilute Excel on your moss (to get rid of the hair algae) you are probably doing more harm than good, and it might be worth doing a little less tinkering, (if you can out up with a little bit of untidiness).
cheers Darrel