more as the salt collects on it. initially, Id guess not much (<10%). As salt (and or algae if its close to surface) collects.....it will approach 60% IMHO. Heat, however, will increas dramatically and immediately. count on as much as 4 degrees within the first 8 hours (for more than 100g). glass tops also inhibit O2 saturation, which can be bad for fish...especially bigger water column fish like tangs. hope that helps.