unable to diagnosis sudden appearance of several clusters of unusual egg-like white

Question
I have had a 40 gallon tank for 15 years.  I did a major water change two days age/ about 50%.  My water is clear, ph and alkalinity normal range,  No Nitrates or evidence of amonia surge.  Today I discovered the sudden appearance of several clusters of white, egg-like spots on the glass of the tank.  I wiped them off and they were round and hard in texture.  My fish look fine tho I thought one fish might have early evidence of ick though none of my friends think it is ick and my clown loach is fine and I know they are very susceptible to ick in a tank.  I have never seen anything like this before and could not find it in any of my fish books.  I am concerned for the welfare of my entire tank and need to know if this siotuation could be a sign of major trouble and if so what do I do about it?  Thank you

Answer
Hi Donna,

Don't be concerned - your fish just tried to spawn! The fact that they were white and hard means they were not fertilized, fertile eggs are amber in color. It's also possible you have only females or a single female, in which case naturally the eggs cannot get fertilized.

You must have some sort of "egg scattering" species in your tank, read the article below to understand about different breeding types:
http://www.aquaticcommunity.com/aquarium/breedingfish.php

Spawning triggers can be anything from a large water change - such as you did - feeding live or frozen foods, and even factors you are not aware of such as morning sunlight. Corydoras for example, are encouraged to spawn by doing a major water change with slightly cooler water. This simulates new rainfall, or so the theory goes.

Look for fish that are especially brightly colored or fish that are acting secretive. Often times a fish that is ready to spawn will look extra vigorous and healthy and be more active.

This website lists a lot of different fish species:
http://fish.mongabay.com/fish.htm
Find your fish and click on them, to find out how they breed.

I hope that helps, take care!
Nicole