Cloudy Hood - Glass Etching

The Rockster

Guru Class Expert
Aug 10, 2007
South Florida

With your vast experience, I was wondering if you ever had this problem, and possibly found a fix.

I am thinking I have this issue. Unfortunately with the bird and cat dander, I need to keep a top on the fish tank.

"If your deposits on the glass are lime, then the CLR cleaner will work, but, I am afraid that what you are talking about may be much more resistant. If you have what I have, it will be clouded glass which is due to etching of the glass and redepositing of the dissolved silica. What happens is that during the day the lights heat the water surface and the glass. when the lights go out, the glass cools much faster than the water does, and so vapor from the warm water condenses on the glass. This water is pure distilled water and some of the glass dissolves in it. Then in the morning the lights come back on and heat up the glass, drying up the condensed water and redepositing the dissolved glass. The dissolved glass, which is silicon dioxide, does not redeposit smoothly. This process is repeated each day, and in a year or so, the glass is badly clouded. This is really tough to clean off, and I have not found anything yet that will take care of this problem, other than replacing tank tops every several years. I am thinking of getting some of those polishing compounds used by people who grind their own telescope lenses and trying them. Another possibility is coating the glass with something that is transparent, less soluble in water and which does not release anything toxic to plants or fish."



Lifetime Charter Member
Lifetime Member
Jan 15, 2009
I must say I've never heard of pure water dissolving glass. Hydroflouric acid yes, water no. It's possible they are correct as RO water is highly corrosive to metals so plastic fittings and tubing is needed in that application but I just haven't run into it on glass before. Have you tried soaking the tops in CLR or vinegar or other weak acids to see if it takes the layer of fog off? Is it on the inside of the glass ( bottom ) vs outside? If it's on the inside it's just as likely to be spray from the tank water which will slowly build up a layer of minerals. Even the odd splash during feeding would build up over time if that is the source. If it's on the outside it may also be the aforementioned dust/debris/dander building up over time.